Well, there’s ProjectDiva.net but to be frank, there hasn’t been a lot of serious approaches towards trying to duplicate the cab feeling.
Part of the reason is how the home console versions use a different approach with two analogue sticks triggering star notes compared to the humongous touch slider on the arcade.
Another big problem here is cost: Neither Sanwa’s OBSA-100UMQ-x-1Fx nor their OBSA-45UK-x-1Fx are to be had for cheap; assuming you’re OCD about avoiding chinese knock-offs, that is.
The most you’ll find is a couple of small-size builds incorporating standard thumbsticks, flush-mounted with the top, paired along with some OBSA-30/45UMQ-x-1Fx, similar to Horis’s mini controller, or something along the lines of this 100mm button DIY build.
Basically it comes down whether or not you’re willing to miss out on the scratchpad/star note) points and how to design them into the system if you want them, no matter what.
For example I’ve been meddling with a pair of OBSA-Y60THO-Y-1F buttons quite a while, trying to modify them into analogue output via hall-sensors plus magnets, but the problem lies with tricking the game into accepting that as valid input. Albeit someone seems to have successfully pulled it off already.
I really ought to buy one of brooks ps3/ps4 boards with their ADC-RxRy/LxLy pins to make life easier.
Jp page already lists an announcement for a new controller, mimicking the hori mini for ps3 so possibly you may be better off swapping the pcb.
(assuming that black plasticy thingie on the top ain’t a touchpad, that is)