Those three kits - Lotus 49, Brabham BT33 and McLaren M7C were originally produced by Heller. Union picked them up and updated the instructions and added a bit of chrome on some of the bare metal parts, but no significant changes.
They frequently show up on eBay (more often Heller than Union boxes), but they aren't cheap in my mind. Prices usually range from $35 to $50, with just occasional low starting prices. I love those kits, and do think they are worth up to $50 or so.
If you are interested in more obscure types, Heller also made a couple of F2 and F3 cars, much less common at eBay. You might find them boxed by Heller, Union or AMT, from USA - all the same contents.
Rick