I'm not aware of any shortage of masks in the UK now. There was at the start. You can buy a pack of 10 FFP2 masks (the EU equivalent of N95) on Amazon right now (ships from Germany): https://smile.amazon.co.uk/medisana-Respiratory-Protection-3...
Perhaps they've not got the US certification and therefore US hospitals can't legally use them? Doesn't stop anyone buying some for their family though.