I just just clicking around on ebay. Found a few. Nice a/c slash knock offs.

https://www.ebay.com/ulk/itm/301935104081


But for 40 bucks! It could he well worth a try. Mayne mod it to breath externally.

I was looking for. 3 inch a/c.

 

Looks good. I suspect a 3" filter would have to be quite a bit longer, to let the engine breath, which will get in the way of your leg. Just a thought.

 

http://www.hammerperf.com/xlaircleaners.shtml#sledge