What parts are nla? There are two sources of replacement DML-01 units, the usual device that caused issues. Other than that aren’t the guts just the same stuff we all get from Digikey/Mouser?
The L-10 is part of the Laboratory Standard Series, the 5C50, et.al. Is part of their top units at that time the Laboratory Reference Series. The 5L15 is the 80wpc integrated amp from that series. The L-10 is 55wpc.
To get better than that you would need to get gear from this century. There are a number of very fine Luxman integrated amps made in the last 15 years.