What do you mean that you cannot buy them? Does it not have the option or does it have the option but clicking it does nothing?

As for colonizing worlds, ensure they are capable of being colonized.

Thats a stellaris thing where you can't buy 'special resources' if you don't currently produce any,

however if you want to produce a decent bit of tibanna you will want to get the 'cloud city' tech and build one on a tibanna gas giant(make sure to delete the mining station in orbit of it, or it won't permit the megastructure) then just build the district that mines tibanna,
Hypermatter you largely have to get from worlds that have the deposit that lets you build a hypermatter extractor, but if you can get an ecumenopolis and give it the refinery districts you get some hypermatter extractor jobs that will produce some.

As to why you can't colonize I figure its your shortage of hypermatter as 50-25 of it is required to build a colony ship in this mod.

Special resources can only be bought on the galactic market. Join the senate and you should have access.
As mentioned above, build cloud city on a tibanna gas giant. Than specialize the city with gas districts and a refinery.
As for hyper matter, some planets have natural deposits. Check all of your colonies to see which ones have special resources of any kind and build the corresponding building; bactra, spice, hyper matter, kyber etc. Also research synthetic hyperfuel. It allows you to build one synthetic hyperfuel refinery per planet. These buildings produce hyperfuel without any hyper matter upkeep. This allows me to sell all of my hyper matter by mid to late game.
I've got no clue as to why you can't colonize planets. Sorry.