The best would be a tossup between the StreetJam OTA-R31, Tamiya TA05-VDF, Yokomo DRB, and Alex Racing CER-D11. They're all front-mid motor design, belt drive with a ton of tuning and adjustability right out of the box. They also don't require too much modification to get countersteer, zero ackerman and high degree steering angle. You can definitely get there with more work from a regular touring car, but the newer cars designed for drift are incredibly easy to drive and pickup.
As for parts and availability, it depends where you live, but unlikely any local hobby shop will stock parts for these cars- the Tamiya TA05-VDF does have a few parts in common with the TRF416, TB Evo5, FF03, so that may be your best bet. Yokomo USA closed up a few years back, and the only vendor in the US I'm aware of is in Southern California called Driftspeed.
There'll be some new drift cars coming out- Hot Bodies TC-FD (based on the TCX) and Tamiya TB03-VDS (front motor shaft drive).
If you've never drifted before and money is of no concern (over $1000 to get started), I'd get one of the aforementioned kits, some spare parts, various pulleys to tune your countersteer ratio, various sets of wheels/drift tires, and read through drifting specific forums, like csjunkies, rcdriftclub and drccentral.