I am looking for a 4x5 film transparency target to use when I adjust my scanner focus with a variable height wet mount holder. I see 35mm format, but don't think it would work well to really set focus. I could be wrong though, but working with a target the same size as what I shoot would make me feel better and I think would work better.

Any thoughts on a 4x5 focus/resolution target and where to get? I can't find them, just the 35mm ones.