I have three full boxes of 12 bore steel shot duck and goose cartridges that I no longer need.
1. 3 1/2" BBs
2. 3 1/2" number 2s
3. 3" number 3s.
For what it's worth, I've found these to be excellent cartridges but don't put them through your Damascus barrels: they are not subtle!
Let's say £30 for the lot, which is a significant discount on the new price. Probably easiest if we can meet up somewhere in person.