How to remove internal sourse from Available source in RSSP

Summary:

Our customer only want to raise requisition buying from in RSSP,

we have already remove the

[Create Requisition for Internal Material Transfers]
Privileges

so in [enter requisition line], customer don't need to select source type, the source type can only be supplier,

but for Catalog Shopping, our customer still can see the internal source.

I want to know how to remove internal sourse from Available source in RSSP

Content (please ensure you mask any confidential information):

We want to remove all the internal source, only can see supplier source in this screen

Version (include the version you are using, if applicable):