Andrew,
It is possible that I may have an air filter as I do have a scrap engine. The challenge will be getting to it, I will get back to you but it may take a while. Let me know if you find one in the interim as the challenge of getting to it is not insignificant. I think I have six cutting decks for the tube frame tractors but at the moment I don't want to loose any. I recently scrapped a 34" deck from my Bolens 850 so I have a few spare deck parts.
You may want to contact Chester Hudson http://www.mdr.co.uk/tillerparts/tillerparts4.html to see if he has a deck. I am sure he will have an air filter if you can't wait for me to get back to you.
I have a PDF parts manual for the 1254, a Tube frame service manual and a Wisconsin service manual plus lots of others, let me know your email address if you want a copy of any or all.
Iain