A number of years ago I changed my calfee from a 3x9 to a 2x11. Really all I did was change the front ring sizes and put a bash guard in the position of the outer chainring and switch the rear cassette to an 11 speed. We recently went on a multiday ride and the chain kept dropping between the front two chainrings on every down shift (upshift was never a problem). It never shifted well before but when we were really tired and want to get to the small chainring it's super annoying when it drops in between.

I figure it's happening because the 11speed chain is narrower (outside to inside not length of link) and the space between the chainrings on the 9speed spider is wider to allow for the wider 9 speed chain.

I've been looking for a new spider as I figure that's a cheaper way to go than all new cranks. Searching the internet it looks like the spider mount is an old Shimano mtb standard. Attached picture.

Any ideas on where I could get a new spider or am I looking at new cranks?