Oops- I thought 1UP had those for sale already, but checking back, the last time he mentioned it was a month ago, when he said:
Update: The 49-way Tron sticks will now use a heavier grommet rather than a spider. However, the spider kits will still be available for use in converting your Happ 49 to a Sinistar joystick. Patience--pricing and photos are coming!
He had previously stated they would work with the Williams 49 as well, here:
Ok, looks like the spider kits are going to be a reality! The spiders will be made of a durable rubber, injection molded with metal inserts. The plate will be mountable on a Happ 49-way with included hardware, and will not change the joystick depth. Will work with or without the Tron shaft. Spiders will also fit an original Williams 49-way with a different center insert (provided). Pricing will be close to my previous estimate. More info and prototype pics to follow...
I haven't seen him say these are cancelled, but I guess there's still no product, so I guess GGG and WW are still the only players in the Williams repro spider game.
BTW, from the pics 1UP posted of the WW spider, and the ones on the GGG site, the GGG ones sure LOOK a lot nicer.