MikeD wrote:I have noticed that 4/3 is available, but I haven't seen 4/2 mentioned (from Southwire, for example).
Southwire's spec sheet for NM cable doesn't list 4/2 or 2/2 NM, so looks like they don't make it.
But you could use copper SE cable. Typically SER (round) is 3 conductors with ground, and SEU (flat) is 2 conductors with ground, although Southwire lists 2 conductor SER as well. Often the bare conductor is full sized, so for example 2 conductor #6 cable with #6 ground would be referred to as 6-6-6 SE. Sometimes the bare conductor is reduced two sizes.
Depending on the installation details and the year of NEC in force, SE cable can be used at its 75C ampacity, meaning #6 copper would be sufficient for a 60A circuit. Under the 2011 and 2014 NECs, this is allowed as long as the SE cable does not pass through thermal insulation. Under the 2017 NEC, all sizes of SE cable larger than #10 can be used at their 75C ampacity.
So if you can find it, 6-6-8 (or 6-6-6) copper SE cable would work for a 60A circuit, unless you need to run through thermal insulation and are under the 2011 or 2014 NEC. In which case you'd need 4-4-6 (or 4-4-4) copper SE cable.