I've also got a 40 breeder with similar temperament of stock and added an L129 Colombian zebra pleco (Hypancistrus debilittera) in the last 5 months. It's a very beautiful fish, but it's very small and in a densely planted tank so sightings are rare. Most Hypancistrus should do really well in a 40 breeder as they are generally 2-4 inches. Bristlenose plecos would also be a good choice but they're kind of vanilla. You could probably find one at Petco.
Plecos are really popular fish to breed so I would see if there are any aquarium clubs or other fish dorks in your area you could contact. I've ordered online from local hobbyists with decent results. Aquatic Arts is also a store I've bought from with great results. One I've not bought from but am interested in is Dan's Fish. It looks like a well run operation and has tons of pleco variety. I'm a serial fish window shopper (in person and online) and Dan's really looks like a good shop. Great variety of all kinds of fish and has a lot of great videos on his YouTube explaining his fish and his shipping and keeping methods.