If you mean a non 300B tube then the answer is no unless you modify it in some way. Cut from a post over at DIY Audio:
"Using other non-300B tubes is risky if you don't modify the operating point (bias) to the correct value. Also the output transformer impedance is designed for a specific tube in mind, so go changing the tube type without changing the transformer is not a good idea."
If you mean an alternative 300B to the stock tubes then yes there are plenty of options out there. Others will be better able to steer you in the right direction on 300B tubes.
"Using other non-300B tubes is risky if you don't modify the operating point (bias) to the correct value. Also the output transformer impedance is designed for a specific tube in mind, so go changing the tube type without changing the transformer is not a good idea."
If you mean an alternative 300B to the stock tubes then yes there are plenty of options out there. Others will be better able to steer you in the right direction on 300B tubes.