Forged pistons options
If you can only find a 10-1 forged slug, then it will have to be measured to verify that it is that ratio.
If so, a Cometic gasket is a excellent option. There a bit pricey vs. the off the shelf gasket but well worth it.
Same deal in the 9.0-1 ratio forged slug if you find one so at least it may be possible to drop it to 8.5-1 or 8.0-1.
I know for fact you can get them @ .100 thick.