LMI and other sellers sells 2nd grade tops fairly cheap (15 dollars or so) and you can test finishing on that. I am not sure if you have size requirements if not you can just buy a brace stock and resaw them into as many pieces as you'd like then just do your tests. The only difference between second grade and others is runout and presence of pitch pocket or knots or other non-straight grain stuff... should make no difference with finishing. The first guitar I just got done (going to Afghanistan too) had a second grade top.
I'm sure you'd spend more than $15 on a trip to the lumberyard and sorting the wheat from the chaff... you can cut it to pieces and do many many tests.