When I took my unit apart to work on a few issues I also investigated the burnt out VU meter lamp situation. Each bulb looks like a very small (diameter) fuse with a lead coming out each end. Both bulbs are connected in parallel and attach to a tap on the 12 volt (center tapped) power transformer winding. I did NOT think to measure the AC voltage going to the bulbs but it will be LESS that 12V. I unsoldered one side of the good bulb so both of mine are now dark.
MCM electronics sells bulbs which look like they will work just fine - in fact the catalog describes them as "level meter lamps". They are available in 3 voltages 6.3V(AC)-Order #25-445, 8V-Order #25-450 and 12V-Order #25-455. Each cost around 60 cents. Absent measuring the actual voltage you could probably get by with the 8V units but I'd try the 12V ones - if they are bright enough, they will probably last much longer.
Charles