Purge valve compatibility?

The purge valve on my 2002 A4 1.6 (ALZ engine) has broken. I can't find a part number on the valve itself, just on the rubber holder which appears to have two part numbers: O6B 133 459 D and PXO 421 212-10. Are any of those for the purge valve? I have searched the websites of the local car parts stores, but I have been unable to find a purge valve for my car: Either they aren't in stock or they are listed as not compatible with my car despite that they look very much like the old one. What might make them incompatible? Are there any differences between purge valves besides the size of the hoses and type of electrical connector that connect to them? Are there any reputable web shops that have this part at a reasonable price? Are there any low quality manufacturer of these valves that are best avoided?