options on an lc smith shotgun?

i recently obtained an lc smith 16 ga shotgun that is in pretty rough shape. the bluing is about 20%, the buttstock is a dark dark brown with plenty of scars and the fore stock is much, much lighter. most of the screws are a little buggered on the corners of the slots. i looked on the lc smith website and it was manufacturd in 1914. it shoots great however. but im having a hell of a time affording 16 ga shells, and is it possible to sleeve the barrels to go to 20ga? ive seen the little skeeters reducers things, pretty much just a bushing, but im looking for a full tube replacement. is anyone aware of any options, ideas?