Try MCB Battery World
I've not bought the 4F22 but I did get a couple of spares for my D1X from them.
This brings up a good point, there are at least 4 versions of that slave. Mine is a YHDC-B, the receiver has a 1/4" jack and uses two AA batteries, they are what I replaced. The transmitter uses a 23A 12v battery, I haven't replace that yet (I didn't even realize it had a battery, I thought it got power from the hotshoe... time to buy a spare). The other versions have different jacks and/or get receiver power differently. You have to choose the model carefully... the numbers are very similar.
One other note. I made the mistake of leaving the transmitter on the hotshoe without spinning down the lock ring. It wiggled out and one of the corners broke off the plastic shoe mount. No problem, but now I keep that ring tight.
By the way this is anything but a hijack in my opinion... good point. I've seen people put [OT] in the subject line to indicate the post was off-topic. Sometimes, like this one, it's just the best place put your post even if it's not germaine to the thread proper.