Personally, I use this seller on ebay for most of my gasket needs
The Gasket Shop
If he hasn't have any listed send him a message, he'll have them
Never had any duff gaskets yet & I have used a fair few sets over the last few years, no premature failures yet.
That includes 2 rover K series head sets & both still going strong several years later.
They also managed to find a set for a friends Ford D series marine engine .... Used 8 - 12 hours a day during the summer months, no problems.
If I go to my local motor factors & order a gasket set, I'll get the same non major brand stuff but at more than double the price
If you want the likes of Payen gaskets, your local engine rebuilder will be able to get them in for you, failing that, it'll be the main stealer.