OK,

Number of problems with some of things I should be able to research but can't. First off is the acid grenade. I've tried everything in the book here but for some reason the 90+ beastmen acid genades I have in my stores appear to be invisible. I've tried the taking them on a mission and dropping them thing, all to no avail

Having allied with the Expedition forces (Don't even start me on them not trading any decent armour!) I only have the rebels to contend with. I was under the impression that I would be able to to run come capture missions on them get get some of the other research pre-requisites but nothing happening there - all the mission are destroy the group or destroy an artifact. Nothing on capturing any of them.

As for Beastmen, I think I have interrogated every class but not all the research options have come out of them. All the capture missions now seem to be for normal beastmen soldiers - this doesn't seem to make any difference! One I'm not sure about is a Beastman "Commander" but I guess this would be a chief? I've interrogated one of them!

I've been through the various research trees available and as far as I can tell I've met the pre-requisites for a lot of technologies (inc. ninja suit, advanced terraforming etc) but I've got zip in available research.

Any suggestions? I'm a bit stuck as some of it I think I need for later in the game..............

My suggestion.....
Do hit and run mission with the intentional purpose of failing your given mission.
That way a new mission will spawn in the territory where you failed the mission and just maybe you'll get a capture mission.