That URL doesn't work. You have to shorten it to:
www.honda-auto-parts-wholesale.com

Once I did that, I discovered two things:
1) A trailing arm bushing is indeed not available for my '91 Integra RS,
but *is* available for the '91 Civic Si. <insert frownie emoticon here>
2) On the home page, all you get is "Honda" in the manufacturer drop-down
box (Step 1), but once you're inside, you can choose ANY make.

Thanks for the link.

These appear to be for the Civic. Are they the same as for the '91 Integra,
though? Apparently not.

Some Googling turned up this site:
http://www.performanceforum.com/wesvann/honda/bushing/bushing.html

Apparently there is this Honda part number:
52385-SK7-N02 (outside diameter 3.352 inches)

I just called the parts guy at my local Acura dealership here in Canada.
That part number comes up on his system, so it IS an Acura part. It's
described as a "bushing, right rear", but he cannot tell from his system
what year and model it's for. The list price is $78 Cdn (roughly $70 US).

Time to call some US dealerships.

Thanks.