Lark M1 Transmitter Needed

A few months ago I bought the Lark M1 with one transmitter. It worked pretty well. I love it!!!  But back then I didn't think I was going to need two of them.  Now, I am in need of a dual transmitter.  Would I need to purchase a full new dual set up?  Or is it possible to just get 1 Lark M1 transmitter and it works with my current TX/RX?

As far as I know, Hollyland doesn't sell sign tx for Lark M1, but they do for Lark Max and lark 150

You could try out the max, it works fantastic