You can make all 10uF caps to be 50V rated that will work fine, they will only fill to max level allowed by the circuit control - first 2 sets of caps will be charged to +17V, next 2 sets will charge to +25V, and final 2 caps will charge to +33V.
LM358 is able to operate up to 36V so you will be fine.
The parts list is from mouser.com they have fast shipping and you can get all parts from them except the circuit board - your local Radio Shack has it. Mouser has lots of enclosures of many sizes to fit your available circuit board.