Red Hat offers a free evaluation subscription for 60 days.
However, you need to prepare HWs and install Red Hat OpenStack Platform by yourself. (This is not an already prepared lab.)
Sorry, you are right. The free evaluation URL is not available anymore.
You can also ask a free evaluation to RH sales people. You can contact RH sales people from "CONTACT SALES" button in https://access.redhat.com/products/red-hat-openstack-platform/