Gobbling Buck,
try some gunshops in your area.
weaver makes a one piece base for for that mossberg 835.
with your reddot bsa, i have one and i got a weaver one piece base for my redot. but the slots on the base don't line up for the bsa reddot scope. so i had to file a notch in it to make the scope fit.since the base is cheap, you can make it fit. i havn't found a scope base for that reddot scope yet. i just mounted mine last week and ready to sight it in.
good luck