Because no one appears to have put this all in one place yet. Posting to c900 category, but contains general info.
Momo, OMP, Sparco share a 6 bolt 70mm pattern.
Another other common pattern is 6 bolt 74mm, but I don't intend to test these.
Momo ML2304 (search for 230835657077, available on ebay) (confirmed on a 1992 turbo, pictured with model 07 wheel)
og9-3: (note, not the same steering column as ng900)
OMP OD/1960FO542A (unconfirmed)
vauxhall corsa C: (popular steering column swap to get electric power steering)
Momo MA6610R (unconfirmed)
I'll keep this updated as I find more.