The bigger the better. I've seen 500W - hugely overpriced in Surplustronic and same on Trademe. Have not seen 1-1.5KW
Also wanted isolating transformer 230-230 1.5KW or more, if it can be dismantled - better.
Also wanted 1.5KW or more autotransformer (sometimes they are referred to by uneducated sellers as step down transformers) which I can dismantle to rewind it. Isolating transformers are normally filled in with compaund and it is hard to modify them.