Jerry, from what I can see, one can model a believable PFE and SFRD fleet with plastic models and kits. But that's pretty much it. Resin offerings had/have much better variety, but as you said, building a believable reefer fleet isn't easy. In fact, depending on where you model, I would say it's impossible unless you scratchbuild or kitbash multiple models.
Take the New York Central's Water Level Route, which I would like to model. Let's use ART as an example. Based on consists for NY-4, NY-8, and other trains that carried large amounts of produce, there would frequently be between ~6 and ~14 ART reefers in a train. So let's split the difference and say 10 ART reefers would be well within in the realm of plausibility for my situation.
Based on fleet statistics, it looks like I would roughly need 6 wood reefers, 2 round-corner DN end horizontal-seam steel car, 1 square-corner DN end horizontal-seam steel car, and one early steel reefer which was quite similar to the R-40-10.
So I would need to build 6 Sunshine wood reefer kits (some of which would need replacement metal roofs; let's say 3-4) and 2 Sunshine round-corner steel cars. The square-corner steel car would be covered by the Intermountain model, and so would the "R-40-10," although it would require reworking some rivets and replacing the door hinges.
And that's just ART, to say nothing of Swift, Armour, Cudahy, the FGEX consortium, Morrell, URTX, etc.
Don't even get me started on MDT. The short version of the MDT problem in HO is that there's no commercially-available M-4 in any form, the 6000 series (the most common MDT composite reefer series at 2000 members) hasn't been available from Sunshine for perhaps two decades, and we need Stan Rydarowicz's end castings very badly to kitbash R-40-23s into MDT steel cars. The result is that, despite the fact that I model the Central, I somehow have over 20 PFE reefers, but only 4 MDT reefers.