Since it has MT2 sockets you can get a wide range of tooling from a lot of equipment suppliers like Chronos, etc.
For vices, etc., you usually find that the smallest version in a range suits the restrictions of the 2A. For example, I find the small Vertex 4" rotary table suitable, but the larger versions would be difficult to accommodate on the table. If you manage to get a vertical head, then a set of raising blocks for the head would be a great help in providing a bit more elbow room under the vertical spindle - once you've got a milling chuck in the socket, there's not all that much room between the end of the mill and the table.
It's generally recommended that you try and get the quill version of the vertical head since it proves to be a bit more flexible, but be prepared to pay more than the value of the rest of the mill if you can find one.
Two small things to say (to the OP): ER collets and 'lowering blocks' for the knee.
Hemingway sell a 2MT ER20 collet holder (which could also be made out of a blank arbor and a bought-in collet nut). The advantage of this is that it will hold up to 13mm and is quite 'short'.
Instead of, or as well as, rasing the head, you might consider raising the body of the mill so that the knee slides off the bottom of the column dovetails a small amount. Admittedly, this may require a bit of thought in possibly extending or repositioning the knee-raising rack, but it works OK on my 2 (not 2A) model with its cobbled-together vertical leadscrew to raise the knee.
If you are desperate for a vertical head, Home and Workshop Machinery
to have one permanently for sale at a price, as someone has already remarked, that is likely to be greater than that which you paid for the complete machine.