I was going to send mine in to Air Venturi for servicing, but UPS wanted over $120 to ship to AV. Decided to try DIY. I just hope I don't have to send AV a bag of parts to reassemble!!
There is a place on eBay UK that has kits for air arms. They list an email address ([email protected]). I would send an email and ask if they have kits or sizes for the regulator. No charge to ask…