I'm unaware of a more filled-out version (and don't see one available on the OCP site), but for a case like that, I'd just make something up based off the guitar chords anyway.

I browsed YouTube and either something exists or they just wrote their own, because it's definitely not what I have in my part. Will probably have to just come up with something on my own...

Ask around and find out if a MD in the area has kept older editions of the keyboard accompaniment books. I've noticed over the years that the publishers are increasingly dumbing down their accompaniments to keep up with the sliding talent pool. As fewer classically trained organists are being employed, more parishes are hiring folk who play in the "fake book" style, using the guitar accompaniment books as lead sheets and making up their own accompaniments.

This is just my opinion, and others may disagree, but even with the new Worship IV, many of the accompaniments seemed stripped down and rather pedestrian.

FF, if you can't improvise in the "fake book" style m'bud David mentioned, I can flesh something out for you maybe tomorrow.
Not to digress too far though, I've always been fortunate to have organists well-versed in improvisation, figured bass accompaniment and "pop/jazz" chordal nomenclature. Pianists as well. It is a skill set that serves a parish very well if one's repertoire is eclectic.

Not taken that way at all! And that is definitely the problem. My part is painfully boring and does no justice to anything, really. Most of the larger anthems we do have big, showy parts so it was a surprise to have this handed to me, but it was the only part the director had.
@melo: never had a reason to do much keyboard improv until this job, but I have learned a lot and I am getting better! Time is an issue and while I would love to write out what I've already been noodling in during rehearsals I don't see it happening. I just got hired for another job (non music but will take 20-30 hours a week of my time) in addition to at least three more orchestra concerts before Easter. Soooo yeah if you are so inclined to scratch something out for me that would be great!

publishers are increasingly dumbing down their accompaniments to keep up with the sliding talent pool.

Maybe not a "sliding talent pool." Maybe there are a lot of little itty-bitty parishes out there, and a couple people can maybe play an instrument, and they play OK. The small parish I attend is blessed to have a very good organist who sings very well. If we had a choir there would be no congregation left in the pews. The parish I attend up North when I have jobs up there *sometimes* has a musician on Sundays. Sometimes. And she's OK.

But isn't this the point of the Common Psalm?

The [Common Psalm] are intended to provide a resource for communities that wish to begin singing the psalm and they can replace the psalm given at any Mass. The texts are arranged according to the liturgical seasons. The intention of the compilers of the Lectionary is for communities to have a core repertoire of psalms that can be used at any occasion. It recommended to start with that a setting is used over a number of weeks or a season to allow the psalmist to gain confidence and for the community to get to know a particular psalm and be able to sing from their hearts.

RS, with all respect to the article' author, I tend to believe that "lowest common denominator" is the ethos regarding the utility aspect of what is provided the public consumer of sacropop accompaniment volumes. A decent, not even gifted, musician (be s/he an organist, pianist, guitarist), ought to be able to adjust to, and flesh out accompaniment strategies according to whatever ensemble combination (or none other than one instrument) they encounter at each occasion.
Though I haven't yet been able to address FF's concern, as an arranger I am left to assume that the piano is the sole accompaniment provider. That affects how I would approach the three basic levels of arranging: the bass note movement, the comping (rhythmic and chordal middle ground) and the exposition of the melody even if further adorned with harmonic textures.
Back in the day, the SLJ's and NALR tried an outreach strategy to provide not only viable but worthy organ accompaniments of their repertoire by having Sr. Theophane Hytrek arrange their tunes, presumably for "organ only" usage. It was disastrous. And that's not to say that organ has no provenance in SLJ style music. It means simply the "lipstick on a pig" approach will fail, and the "pig" is not necessarily unworthy.
There's ensemble, and there's ENSEMBLE. Even if you don't totally respect the genre of a song, it doesn't mean you don't put your best foot forward. And if there's no ensemble physically, then the arranger ought to provide as fully-realized keyboard accompaniment on either instrument that best supports the text and melody. YMMV