Just found a good link on DP adapters:
https://www.sapphireforum.com/showthread.php?28155-EWP-Guide-3-or-More-Monitors-Eyefinity-Setups-and-You!!
BTW, most adapters from know eyefinity capable graphic card manufacturers seem to be identical and can be used when they show the eyefinity logo on the box. We have tried XFX and SAPPHIRE with good results. PNY, HIS,... should also work.
Best regards
Rainer