I had trouble locating a supplier for this filter. Two false starts then found a supplier in Fife.
This company has a few in stock and hopefully more coming from the US.
This is their details:-
Jays Performance Ltd
Unit 4 Elgin Works
Dickson Street
Dunfermline
Fife
KY12 7SL
United Kingdom
Email:sales@jaysperformance.co.uk
I have no affiliation with this company.
Also fits the Bantam d14/4 b175 but please check for yourselves.
did you try, K&N importers in England? usually have good stock
https://www.knfilters.co.uk/?gclid=EAIaIQobChMI1s_H8uPG5QIViUPTCh1DqAzfEAAYASAAEgKSz_D_BwE