It's pretty easy to make a relatively(not laser accurate but good enough) accurate toe gauge, seeing as a toe is about all you can adjust on a standard mini.
I found being able to set your own wheel alignment invaluable as you don't have to decide on a setting but can experiment with it to get it handling as you like.
To make the toe gauge:You need;
A couple of pieces of square tube that will telescope nicely,
A couple of pieces of steel rod,
some nuts and bolts...
and a welder
The rod goes through a couple of holes drilled in the ends (one in each tube) of the square tube, they don't have to be excessively square so don't stress too much.
I also cut off a one section (about 1cm or so) of the outer tube and welded a nut and a screw/bolt to set the short measure I welded another to the outer section so you can set the long measurement as well (not essential).
To measure the toe:Do the short side first (rear if setting toe out, usual on a mini) do up the locking screw on the short section, take it out and do the front the difference between the short(the locking screw you did up) and the other outside tube is your toe setting...
You want to put the rods on a known point on the tyre / wheel like a tread groove(doesn't have to be the middle) in line with the centre of the wheel viewed from the side.
You need the car on the ground at it's intended ride height as explained above.
A couple of photos (click the links) probably explain it better...
https://goo.gl/photos/JosNeARajND6QZig8https://goo.gl/photos/jAmA1qEbsLLnc22q9