I guess, it's because of the odd size...
the 290 was dropped by honda (I only find very few references that it ever existed)
it was closer to the gx340 than the gx270 according to what spareparts match..
your predator 301 is a re-labelled Rato R300 just like the preadtor 212 is a re-labelled Rato R200..
but if that helps finding aftermarket parts *shrugs* IDK...
good luck though
'sid