I guess 22watts 8 ohm is not a common value this as near as I've got so far.
25 Watt 10 Ohm 5% Gold Tone Aluminum Shell Wire Wound Resistor | eBay
I'll keep looking though if you agree I'm on the right track.
edit
getting closer
2x 20W Watt 8 Ohm 5% Wire Wound Cement Power Resistor | eBay
No, go for the 10 Ohm 25W. I am assuming the amp has a 4 Ohm tapping? If not use a 22 Ohm 20wattish and run the amp at 8 Ohms. 22R should still save its bacon.
Dave.