If you want a heavy duty cover that will last for years and don't want to goof around making it yourself allbrands has good cotton duck covers.

http://www.allbrands.com/products/abp15543.html

I have one on my board and love it.

I took a class from a national quilt teacher and one of the things I learned was for quilting you want an ironing board cover with some grip, not the slippery silver stuff. It keeps your block parts from distorting.

I have found ironing board covers at Target and Walmart in every size. I can buy the extra large size to fit my over sized ironing board, it's plain muslin, not pretty like some of the other covers. I bought a Steady Betty and could kick myself for not having one years ago! Didn't even know what it was until I read about it on this board. It's the best ironing surface I've ever used for quilting.

The last time I looked at a local Walmart there weren't even any ironing boards. They certainly didn't have a cover to fit my 18" x 48".

What's a Steady Betty?

Check Ebay

That's what I do!

I didn't find any 18" x 48" on there.

I made my own too. I used Insul-Bright underneath the fabric.

My ironing board is oversized 18" X 54". I love it but when the cover started to tear I searched all over for a new one. Even bought a few thinking they would fit and had to take them back. Finally made my own. Used teflon fabric (that silver stuff. Bought 1 1/2 yds with my Joanne's coupon. Placed it on my board, cut off some of the excess and sewed the edge. Fits great and cost me about $7. I'm happy.

Any of the ones that fit the rectangle boards should fit your board. You'll just have to pull the cord tighter or use thumb tacks to tack it to the back of your board.

Mine is a weird size too. It's an old antique wooden one. I have a regular one too but it's so flimsy and unstable compared to my heavy wooden behemoth.