Which size mighty mounts?

i just wanted to thank everyone for their help on the roof rack. I purchased the complete OEM Yakima rack for ~$275 shipped. My next questions is, which Mighty Mounts fit on the wing bar? Can I go to my local REI and purchase, or do I have to order from Isuzu? I need the vertical mounts for a ski/snowboard holder.

Thanks in advance.

Part number 2-90116-821-0 wing bar mighty

as per the invoice.
I got mine from St. Charles Isuzu. I could not find them at REI or where ever locally. Sorry.