Welcome Aboard the forum. While you may find an inmate up here willing to sell one, genuine Walther TPH .22 magazines are Rare Birds and not easily found. The blued magazines for the German guns are even rarer. I recommend watching eBay (three for sale right now) or gunbroker.com (one for sale) and be prepared to pay a premium. Do not buy a .25 magazine, which are more readily available but won't work. You could try Triple-K, who sell a third party magazine recognizable by its extended finger rest. They are of varying quality, a few swear by them most swear at them.
You've got a sweet little pistol there, and there are a number of us up here who own and enjoy them. Again, welcome.
Gonzo.. is right on about TPH .22 magazines. You are going to have to step up and pay. Note that you can use the plastic base and the magazine spring from the .25acp mags to keep your .22 magazines in good working order. I am not a fan of anything but a real Walther magazine in my TPH.