I think your only option will be a parts machine or from someone who disassembled and is selling the parts separately. Here is a pic of a whole machine, so you can see what the tension assembly looks like. You are blessed to have the shuttle included. Not always easy to find. Slideplates can be made of varied materials such as hotel keys, old credit cards and the like.
I actually think you have most of the unique tension assembly and might be able to get away with a common honey comb spring and hand nut, even though the MW hand nut looks different. Do you have other machines from which you can try the spring hand nut?
Update: the Singer beehive spring and hand nut are too small.
What you need is the same as on my Plymouth and Graybar machines, although the hand nut for your machine looks different. It is concave, mine are solid and rounded Still think it would fit.
http://www.ptciclassifieds.com/listings/1349336/
Hope this helps.