countryboy,
To my knowledge the only accesory out there would be an aftermarket stock, and a rifle basix trigger.
I bought a brown laminated one from Marlin and sanded the barrel channel out to fit the heavy barrel and it looks and balances much better, at least for me.
I think that Richards microfit also has some after market stocks for marlin rimfires.
the rifle basix trigger can be had at cabelas and probably brownells or some of the other firearms supply places. It it spendy though.
Timney is rumored to be coming out with an aftermarket trigger, but I guess we'll have to wait and see.
cowpoke