If Jotajoe no longer makes them, someone posted a detailed drawing on this forum a couple of years ago (I'll see if I can find it). You could use the drawing to make one. If you don't have the resources to do it yourself, take it to an engineering shop and get them to make one for you.
Here it is (attached as a pdf). I must have downloaded the original CAD file at some stage. I just converted it to a pdf file.
I dunno who drew it, but thanks for sharing.
Hang on, I just found another drawing (picture below) that someone produced. It differs slightly from the pdf drawing in that there's a recess milled at the top of the bracket to make it a bit thinner. As far as I recall from fitting one of these things about a million years ago, the recess is necessary for it to align vertically on the bike.
You'll also need a spacer (about 25mm long) to go between the plate and the engine mount in the middle hole of the bracket. Sorry, I don't have the exact dimension for the spacer or the length of mounting bolt required.
I assume the bracket shown in the pdf drawing uses a slightly longer spacer so doesn't need the milled recess for the footrest boss. That would make it simpler to fabricate at home.
There has been upgrades to the Bushman/Lawton sidestand brackets over the years. The first brackets needed the center stand removed or the tang modified. Keith suggested moving the stand mount holes as shown in link. I did this to my Bushman bracket and it worked well on my bike and I can use either stand with ease and did not have to cut the tang on the center stand.