The old Rogue Trader beakie plastic marines are very difficult to get hold of. You might get lucky on ebay.
As to the tanks they used the old plastic Rhinos and Predators, again these are also out of production and I doubt your be able to get the sprues (even on ebay). Your best chance is looking for already built and painted tanks and re painting them.
As to weapons the old Rogue trader Rhinos had two bolters instead of a storm bolter, and the Predators had an autocannon turret and lascannon sponsons (no heavy bolter ones that I can remember on the old plastic kit).
There is also the old hamster ball land raider, that had bolters and on the capolla and lascannons on each side. No Heavy bolter mount like the current one.
The land speeders were the open front flying chair style, these were all metal. You might be able to pick some up on ebay.
I'm afraid I don't have any pics of my own ones as I sold them ages ago.
Google it though and I'm sure you'd be able to find some reference photos.
Good luck!