I have yet to find Mothers R3 in a local store. Seems like it might be some sort of a specialty item, maybe available at race/track shops but not regular distributors from what I gather. I wound up ordering it online, waited until one place had a free shipping sale (since the shipping was going to cost almost as much as the R3!). I noticed that Amazon often had it, but only in a 6 pack box... I suppose if you found a few friends locally to split it that might make sense.
I've used both Premier's TTR and Mothers R3, both have worked well for me.
Golden Gate BMWCCA - Car Control Clinics
'13 C4S/'12 328i/'04 GT3
Past: '09 M3 DCT/'03 M3 SMG/'95 M3... missing an E30 I suppose...