Wanted: Karma jockey wheel

Decided to strip and clean an old St. Etianne that has been sitting at the back of the shed for a while with a view to sell it on. Upon stripping the rear mech I found that one of the jockey wheels has been destroyed! Tried some spares from a Shimano mech but they do not fit.

The mech on the bike is a Simplex.

Does anyone have a spare or two I can have for nowt to get this thing back on the road?

(Not in London so will need to be posted)

I have 11T alloy, only 6 grams with ceramic bearing.... maybe it will fit... try it in WC1