While I was on my trip, I swung by a store called Two Kings Gaming. The reviews I read suggested that customer service was rather low on their priority list, but I figured I had nothing to lose.
The store mostly caters to Magic : The Gathering, and Warhammer 40K, but they do have a decent selection of out of print RPGs (primarily D&D, but some other systems). 2e is probably the one they have the most of, although 1e and 4e weren't too far behind. Oddly 3e seemed to have very little. As nothing beyond 1e really interests me (except 5e), and I have all of the 1e stuff I care to have, I wasn't holding out much hope of finding anything.
To my surprise, I found a copy of Holmes D&D for sale, tucked into the rack with the White Dwarf back issues.
My copy of Holmes is rather pristine, so I have been considering buying a "reading copy." I couldn't find any price, so I took it up to the counter expecting to be ignored (based on the reviews I had read). Instead, I was waited on immediately, and even better, although the price was $24(way overpriced), they sold it to me for $10 (much more reasonable).
Next time I'm up in WNY and I've got some time, I'll head back to Two Kings Gaming to see what they might have gotten in.