and getting any pressure to build up at the lever
If you are getting pressure, and holding the lever it doesn't sink to the grip... the M/C is fine. If you want to do it anyway, the bore size (5/8" IIRC) is molded into the casting by the outlet. Pretty easy to purchase a quality kit from anywhere. Probably not a bad way to spend $20 considering its age anyway.
If you are having trouble bleeding, heres some tricks:
1) Check
both ports of the M/C. You have the return port and next to it is an equalizing port that is real tiny. Stick a stainless wire/ welding tip cleaner/ jewelers drill bit, something to clean it out.
2) Temporarily rotate the M/C on the bars so that it is as level as possible while bleeding.
3) With pressure on the lever, crack the banjo bolt at the M/C outlet to bleed there. This works 90% of the time for stubborn systems like MV Agusta.
4) Give it time! Fill the M/C, crack or remove the bleeder, grab a beer, and just wait. Note that any buddy calling you about rubber banding or zip tieing the lever closed is wrong. Period.
5) Vacuum bleeders are great but you may need to seal the threads of the bleeder to make it affective. Teflon tape works best but be careful to not cover the hole in the side.
6) In the most stubborn cases, theres the option to remove the caliper, hang it well above the bars (bleeder still up) and reverse gravity bleed it.
Good luck!