Alumacraft offers them as an accessory. Maybe go to alumacraft.com and drop them a note. Otherwise, maybe do a general google search of bow trolling motor mounts -- a lot of the hits will be TinBoats.net threads. Yet another options is contact Fish-On Fabrications (another TinBoat sponsor). The mount should be fairly straightforward so I imagine they could bend some aluminum for you fairly quickly.
Hope this helps.