you're not the only one. I'm planning for this as well, but no time soon.
You'll need to use Google, and then see if those guys will send you their drawing of it, and then get it custom made. No one makes one for purchase. Unless of course you can get your hands on a KL motor and a Miata trans, draft up the adapter yourself (like I plan on doing) and THEN get it custom made.
Now with Moderator power!
Black '93 BP RS - wrecked, parted, scrapped.
Green GS - Sold.
Black GS - Summer DD/Race car - Fancy KLZE
Red GS - K8-ATX -> MTX-KLDE - Frakencar. Scrapped
White GS - Rusty. Parts. Scrapped
1997 BMW M3 - my summer baby
2002 BMW 325Xi - sold
2003 Forester Xti - EJ20K swapped. Feedback