Paul, I think *any* jfet will be more than adequate for source follower application here.
Nothing magic about the J102. The main question will be Idss, but even that isn't terribly critical. A higher Idss may require a larger source resistor, but that isn't all bad either.
The low Idss of the J201 can be helpful when the D104 is powered through a 9V battery. Even with heavy use, the battery will pretty much last its shelf life. Of course, not a concern when the preamp is powered from a mic jack.
I did find what may be the last big stash of SOT-23 cased Fairchild J201s through AvNet, one of the big industrial component suppliers. Cost is about 17-cents ea. in small quantities. I ordered 200 and the price dropped to just 11-cents ea. If there's little fear of SMD work, this may be the last chance to get known-quality devices at a reasonable price before the "bottom feeders" take what's left of remaining stock, then sell them at $5 ea., or more.
Linear Systems is making some high quality low-noise JFETs like the 2SK170 -- now called the LSK170. Prices aren't cheap but not unreasonable either. I guess we should be happy to have a source of high-quality parts in both TO-92 and SOT packages.
Attached is a virtual reality image of the SMD version of the FET Transformer board with mounting tabs. Before ordering, I'm tempted to add a line of unplated "vias" along the tab lines so they can be easily snapped off for use with other crystal mic types or other audio and RF circuits where a source-follower is needed. The board density is high with short trace distances so it should work well into the VHF region with the right FET and use of the poured ground plane.
Paul, W9AC