Almost all the terminal blocks we use are 3.5mm. We use only Chinese brands, which are available in China and are significant cheaper than the American brand names. You can imagine if we would pay $5 per pair of connectors, and we have 10 pairs on each board, how much we would have to charge for the boards...
You can find some equivalents here:
In our experience, not any plug fits any socket (with the same pitch and number of pins, of course). There are small variations in design which makes them incompatible. So we have to buy both the plugs and the sockets from the same factory.
Tell me what you need and maybe I can help.