I called Masterbuilt and they are sending me a cover for my 40 in. $29.99 plus shipping. On a side note, she also said when not using the smoker to take the control unit off and keep indoors as it is real sensitive to temp and moisture. Nice little piece of advice.
I got a generic cover for a vertical smoker for my MES 30 at Home Depot for around $10. Fits the 30 and has an elastic bottom for a snug fit. It's a tad longer than the 30 is tall but that's not a problem.
I just found one at lowes that fits my MES perfectly. It must be the same one scubadoo97 has... It cost 7.99 and has an elastic bottom so you can tuck the powercord inside easily and protect it from rain.