Congrats on finding this pair in black! Finding correct knobs will be hard. The NEC versions (AUA-8000 and AUT-8000) will fit, but will be a matte black finish (no chrome ring on the edge), and have a flat portion on the knob. You can use knobs from the MCS 3835, 3845, and 3701 - and they will fit & match, but they will have larger plastic inserts - so they won't be as heavy. All of the matching cassette decks used small knobs - like the variable output on your 3710 tuner.
Some of the MCS 3837, 3847, and 3700 will have the same knobs as the 3835, 3845, and 3701 - but some have the matte NEC version with the flat portion. I've never figured out why - I think it depended on which box of parts they were pulling from at the factory. So, if you find one of those - look at the style of the knobs carefully.