The retail versions of those adapters ship from the factory with full-height adapters installed and low-profile brackets in the clear plastic clamshell. If you bought the adapters new, you might have purchased an OEM version that only had one bracket. The brackets are not available separately. I would advise contacting the seller about exchanging or returning the adapters, so you can buy adapters with the brackets you need.
I'm having the same problem inverted (i.e. I need low profile brackets and am sold full height ones). The seller is saying their suppliers say it's not possible to change them. I'm not really sure why there are all these difficulties to get the right brackets and why they are not sold separately. It's such a silly piece of equipment.