A couple of stores here in the Seattle area typically have the more rare Plecos; The Fish Store and A Place for Pets. I believe they get them from The Wet Spot (Retailer/Wholesaler) in Portland.....you might start there.
Did you make it to Seattle for the GSAS meeting last month, we had Barbie Fiorentino as our guest speaker? She is a Pleco breeder (and LFS owner) of national (and international) renown from Spokane. I am not into Plecos, but she did a great talk which is available for members to download from our GSAS website. You can join online with Paypal.
75 Gallon, 2X55W AH Supply CF 8800K, 1XFluval F&P 2.0 48"/59W, 2X Marineland 350 Magnum filters; 45 Gallon Tall, 96Watt AH Supply CF 6700K, 1X Marineland 350 Magnum filter; 30 Gallon Long; Fluval F&P 2.0 36"/46W, Marineland C-220 filter; 20 Gallon, 1X26W AH Supply LED kit, Marineland C-160 filter; all with Press. CO2 and (Calcined) Montmorillonite Clay
Greater Seattle Aquarium Society (GSAS)