Gary, sorry for my earlier comments, but the fact is that the amplifier that you discussed in your other thread is just one gawdawful circuit and will not sound good. I don't mean to put down tube amplifiers in general. I've built a few myself, and some of them sound pretty good. (In fact, as I type this, I'm listening to some internet radio played through a tube amp to my desktop speakers.) I'm just saying that there are a lot better simple tube amps than that one that you are interested in.
If you really want to build this amplifier, then take Canadaelk's advice and pick up a used transformer. There are lots of them around for little cost.
A transformer suitable for your circuit is readily available in almost every old 5 tube AC/DC radio that you'll find in a garage sale, dirt cheap.
Build the circuit, see what you think. But don't spend a lot of money on it.
And by the way, I don't know where you got the 10 watt spec from, but you don't need a 10 watt transformer for that tube.