You have checked all the usual places for this code, if it's not there, you'll need to now contact eBay Customer Services.
They'll provide this essential code for you , and be aware you have 7 days to collect the item after being notified it's in store.
This is the easiest and quickest way to contact eBay Customer Services, for a Call Back option.
https://www.ebay.co.uk/help/eua?id=5275&mkevt=1&mkpid
Lines open 8 a.m. - 10 p.m. on weekdays
9 a.m. - 6 p.m. on weekends.
Automated agents will be available on chat outside of the above hours.
I recommend contacting CS first thing in the morning as there's more chance of Dublin answering.
@kygr_3798