Why not build an attenuator and use it with a 6V6, you’d get low output from the speaker and as long as you limit the attenuation to about 12 db you’ll still get the cool 2Stroke tone. Gerald Weber wrote an article in Vintage Guitar Magazine some years about on how to build a 6db attenuator and then again some time later a slightly fancier version with a switch to select 6 or 12 db of attenuation. I build both, they were both super easy to build and work great. There is a “how-to” tutorial on building the two stage version in Weber’s “All About Vacuum Tube Guitar Amplifiers” book too. There are probably other DIY attenuators online.
Probably cheaper than a new transformer and would give you more output options.