You can flip your Beseler to project on the wall. Murphy's Law requires, though, that the facing wall be either too close or too far away for your purposes.

Try a 35mm or 28mm fl camera lens, you have nothing to lose. If you are only enlarging a spot in the center of the field then flatness is a non-issue. There are few lenses that aren't acceptably sharp in the middle at f8. Temporary Beseler boards can be made from chip-board, masonite, thin poplar, or even black foam-core. Attaching the lens can be a bit tricky if you don't have a flange. If you can get hold of a T-Mount lens then the T-Mount adapter itself can be used as the retaining ring to hold the lens to the board.