Yes, this is true (you need a ROM archive sites) but the stuff on those sites is normally just hardware ROMS discontinued and unsupported by the manufacturer so the only way you can use the synth is with an emulator or second hand unit (where you would probably need to go to a ROM archive site anyway as the OEM doesn't support it).
The Devs did contact all the hardware manufacturers and offer to work with them, I for one would be happy to pay for and use a supported ROM, but it seems they were not interested in being involved with these older unsupported products...it is what it is right now until something changes but it is fascinating seeing what can be done either way. Aa fun as it all is, there are now better software alternatives for all of these older legacy synths IMO (even the Ti) so it really is either just a bit of fun or a way to use old patches (if you had the hardware)