You should be able to get the schematic and or service manual using a search engine.
Private label transistors indicates the vendor expects you to take the unit to an authorized service shop for repair, or at least buy the parts from the OEM.
What one ordinarily does, is 1. Determine if npn,pnp, junction , mosfet or jfet transistor.
2. determine package size.
3. determine maximum voltage that could occur c to e or s to d. This can usually be determined by the voltage rating on the capacitor suppling c or, s or d.
4. determine pinout, where the base or gate is. The input drives this.
On distributor website, one then selects polarity under single transistors, junction or fet as appropriate. then clicks the minimum voltage in Vceo, polarity designation, package size, in a selector table. then inspect what is available.
Maximum voltage selection will keep you from looking at a lot of television & industrial motor drive transistors.
Warning, 3 mhz & slower Ft transistors sound bad on high frequency musical content in input, VAS, and driver positions. IE high freq performance doesn't matter on voice, guitar, electric bass, does on quality wood piano and some high freq percussion instruments. Where the recording engineer didn't eliminate such "distractions" for more punch.
Hint, a Carver PM-1.5 schematic I have has no fets.
You've given us none of above.