If it isn't a commonly available part that every gun store potentially carries (think AR-15 parts) and after searching you haven't been able to find it then my recommendation would be to try and contact Marlin directly and see if you can order the part/s you need. Though I am pretty sure you don't need an FFL to order a new bolt to be safe you could always work with a FFL dealer to negate that hassle.
numrich has a new style and old style breech bolts for the marlin 80E but both are showing sold out at this time, but check back or send them an email and they should let you know an idea of when they will get some more in stock