The thing about the TB-303 is that the key to its sound isn't necessarily found in the synth part of the device. The SEQUENCER is the important part; the way it handles legato, the way the "glide" function works, etc etc...all of that is where we get the "acid house" sound. It's worth noting that when users were modding their 303s back in the 1990s during the ACIIIEEED craze, those mods generally were done to expand the synthesizer, and the sequencer would be left alone for the most part.
However, I should note that I'm very much a TB-303 hater...not because I haven't used them (I have, quite some time ago), but because I could NOT see the point of dropping up to $3k for a plastic box that really only did about 7-8 things well. That, and the fact that that sound (as well as the infamous "Juno Hoover" as well as the M1 House Piano) was super-played-out unless the machine(s) were in the hands of someone who could wring something amazing out of them through adding effects, modding the synth (such as the famous "Devilfish" mod), and doing something other than yanking the batteries out to generate sequences. So I'd suggest following nickgreenberg's lead here and going with a software version...by using a VSTi version, you open up the 303 to control capabilities that the hardware sequencer in it could NEVER do, plus the sound is super-easy for a VSTi to replicate without massively upping your CPU load.