Sampling a piece of gear or an actual acoustic space is something you can do yourself. You can make location recordings using the equipment of your choice, edit a bit afterwards and use the complementary application Altiverb IR Pre-Processor to make them into Impulse Response presets.
All the info you need to do this is in the Altiverb Manual chapters 9 10 and 11. The Altiverb manual.pdf is installed by both the demo installer and the full installer.You can find a quick overview here
In addition we will be happy to help you make your impulse responses. Do not hesitate to contact us at firstname.lastname@example.org if you have additional questions, or if we can be of assistance.