Would expect that Take 50 shows up under the command
show installer packages
What do you see when run that command in CLISH on the VSX box.
Does it show anything at all for available packages.
Take 76 is an ongoing so won't appear by default as available as only recommended packages appear normally. You would have to import the link for Take 76 manually.
As suggested check that can actually connect to the Check Point update site
sk83520 is the one you want for checking connectivity for various updates