I'm not sure that I'm understanding the question or the geometry of the assembly. Are you saying that you have a 1.75" shaft that is slip fit in a brass bushing that is press fit in a 2.5" tube? Are you then saying that the only replacement bushings that you can find are 1.75" x 2.625"?
If that is the case, I would expect that the replacement bushings are being sold
with an oversized OD on purpose. I would think that it would be optimistic to assume that a press fit dimension on a tube in a marine environment
would remain within spec's after several years in service
. I would expect that in many instances it would be necessary to use a replacement bushing with an oversize OD in order to get the necessary amount of interference
in the fit. Skimming the OD of a brass bushing to a precision dimension is a common job at most any machine shop & usually does not cost very much.
If you just want to buy standard 1-3/4 x 2-1/2 bearing tube, it certainly is available.
BUNTING BEARINGS Sleeve Bearing, I.D. 1-3/4, L 6-1/2 - Sleeve Bearings - 12D368|CB284052 - Grainger Industrial Supply