There's nothing odd about 22 x 24. It might not the most common, but it's not odd.

There are dozens and dozens of "normal" sizes. Retailers can only carry the very most common in the store. Be a little more resourceful (like a Google search) and you'll find plenty of choices.

Once you latch on to a source you like, consider buying several. You'd do better changing your filter several times a year rather than once every other year.

Thanks for the response. I had already located several on Amazon (I'm resourceful - that's why I'm here!), but it is not normal in my experience not to find something in the big box store.

Hmm, well I guess different people have different experiences. I often DON"T find what I'm looking for. The large store chains typically stock only a small fraction of what they sell in the stores. The rest you find on their websites and they ship (usually for free) to your local store for pickup.

Failing that, everyone knows how to find multiple online sellers of just about anything.

For manufactures to have dozens of filter sizes is not only odd,it is outright stupid and totaly overlooks the consumer's ability to properly maintain their system. I have bought hundreds of hvac systems by various manufactures over the years and asked every factury rep at one time or other to give me sound reasoning for so many filter sizes. Not one was able to make sense of it. The most often response was"well,the different case diamensions just work out that way". My posistion is, there is no such thing as too large and in this example,the desighn engineer says the handler needs 528 sq inches of filter. A 20x25 (available any where) is 5.3% undersize which is negiledgable. Ok,so let's say the engineer refuses to sign off with less than 528 inches. Use 2 16x20 filters(available everywhere) for 640 inches in either a vee or slanted rack. A secound and even better way is to ship a 25x25 = 625 inches (available everywhere)filter rack with the handler to be installed in the field. The filter rack is simple to open and close without tools unlike most built into handler case arrangments. Let's assume the "bottom line guys"say no way. Guess what ! There is an even better way still. Build in a 20x20 rack and slap on a sticker that says "USE ONLY 20x20 PLEATED FILTER". That's a whoping 1600 inches. I see the wheels turning behind those shifty little eyes and you thinking "now see here Klem,you can't just go telling folks how to build their product". Well any contractor that installs the handler without offering a customer the option of a ceiling or wall mounted 25x25 filter should be hung up by their heels on the public square and severly whipped by two ugly women.
Who wouldn't pay $50 extra to be able to stand on a step stool and change filters instead of going in the attic?
Odd? I say it's beyond odd. Home owners should not be expected to search the internet for a source of filters.