I’ve got a new XL frame on the way with a tall seat mast. I’m pretty sure a standard 100mm shim is not going to be long enough to have the seat post well supported by the top/seat tubes. I’ve cracked a similar frame at the top/seat tube junction before despite having a shim with the minimum 100mm insertion so don’t want a repeat! My backup plan is to glue two plastic USE shims together but its not an elegant solution so I’m looking for a decent length 31.6 to 30.9 shim. Anyone have any ideas?

If no stock options show up, you can get a sheet of 0.3mm brass and roll it yourself. It’ll be a pain to fit though.