`BSA SCORPION SE 22 CAL

A couple of things you might consider.

Contact BSA and ask for the size. An email reply may not happen till early next week. Lots of O-Ring warehouses to purchase from here in the US. 

I use https://www.theoringstore.com/store/ low prices fast shipping. 

Contact http://www.airgunspares.com/store/product/9456/BSA-Scorpion-SE-Seal-Kit-Part-No.-Complete-Set-of-15-Se/ I have purchased a couple of items from them in the past for my R10. This is a complete set I believe and you are looking at about $16 USD + shipping and probably about 2 weeks delivery but you want to confirm ETA with them.

I used to use XTAIR.com a lot for my BSA parts but sadly they have closed due to the pandemic.

What is Air Superiority called now? Nitin Nelapudi (NICK) ? He should have all the necessary parts to service BSAs.