These are links to DIY audio and supplier's pages that I have found useful
Kenji Mizushima's wonderful web site single-ended dot com was the source of my inspiration to enter the world of SE triode amps.
VT4C is a really good supplier for things like transformers, chokes, valve bases, tagstrips, high-quality phono and speaker connectors, etc. They are based in Hong Kong. Unlike most miserable suppliers they have real 240V stuff. Here in Oz, where my domestic mains is 245V, I really have no plans to use "220V" transformers. Custom transformers are essential if you don't live in wonderful USA and you have 245V mains. I bought my KT88 iron from them, and for the DHT amp, they made a special order mains transformer. I've since bought two special order R core transformers from them and both quality and price are very acceptable. Essentially, they can wind any transformer within the scope of core power and a given number of lead-outs. Speak with Sandy at VT4C.
My 2A3 / 300B amp transformers, chassis and chassis hardware are from the excellent Taiwan company James Audio. They will ship directly at much lower prices than buying through overseas distributors but you need to pay by TT. The products are very high quality. James' Ms. Shirley Wu is friendly, easy to deal with and always provides good information.
My KT88 amp chassis, Shuguang valves and a few other items such as some capacitors were from KUK Audio in mainland China. Peter is the contact person and always responds quickly and accurately. They will ship globally by EMS.
Mrs. Mable is a well-known supplier of many DIY valve audio parts based in China. She also ships by EMS and responds quickly and reliably. Many of the small parts as well as my Guiguang and Psvane valves were supplied by her. Guiguang are of course now defunct (and replaced by Psvane).