Is there a third-party source for SPARCprinter consumables?

Yes, there is. The SPARCprinter is OEM'ed by Xerox, and uses the same
consumables as the Xerox 4030 laserprinter. The appropriate part
numbers are:

Toner-cartridge: 365-1124-01 Sun
6R281 Xerox

Drum-cartridge: 365-1125-01 Sun
13R32 Xerox

Fuser Lubricant/oil: 370-1371-01 Sun
94E95090 Xerox

Fuser wick: 811-1687 Sun (Sun Express)

These parts are available from various resellers.