You have a few options. You can deploy the MSE Runtime Server and MSE Catalog Server to each of your two NLB'd application servers.
From here you have two options. 1) Each runtime could be updated to only use it's local instance of the Catalog Service, or 2) each runtime could use a DNS name to access the catalog service that the loadbalancer would route calls for.
One additional option would be to install the Catalog Server to the database cluster and register it as a generic service so it fails over with the cluster (but could also potentially initiate a failover itself).
You can judge the merits of each approach based on your solution.