Ok... I'm not going to recommend any since I don't have direct experience with them... but I have tried to pick from known good companies.
The first I came across is a 35" Waco by Dumas for an electric motor ... it's under the 40" mark but since it's a biplane, it'll still have 70" of wing between the two wings... link is at Tower Hobbies here
Dumas Products, Inc. Waco YMF-5 Kit, 35" | Tower Hobbies
As it turns out... I'm not finding many decent balsa kits or even ARF's... I guess with everyone getting premade foamy's for whatever reasons they have... the balsa kit market is pretty slim now. It's a real shame since no foamy is going to fly as well or look as good as a balsa or fiberglass airplane. Of course biplanes were also not big sellers and limited in selection to begin with.
I guess the least I can do is provide a Google search that I was using to look for them...
rc balsa kit biplane - Google Search
I may look for more later but have a few things to do first... I love balsa kits and ARFs and biplanes are always cool. I'd also hate to see you have to go with a HobbyKing selection since they may or may not be of good engineering despite their looks, it's just a gamble that I hate seeing people take unless you've found good reviews on the specific model they may have.