Please see information on joining them here: https://www.disabledsg.co.uk/
Here’s some info from the Disabled Shooters Group’s Chairman Ben too…Gun hire is possible but you are right an accompanying license holder would be required, however a license holder will probably have a gun that the non license holder can use. This is a slight grey area though as the license holder should have insurance to cover themselves and the non license holder so to begin with coaching sessions are the best way until the individual has a license. Just for informational a license with suffolk constabulary is £79.50 and lasts for 5 years.
Membership to the Disabled Shooters Group is £10 for the first year, which comes with a range of benefits; the main two is 20% discount to all DSG events (so coming to one event normally saves you the cost of membership) and discounts on cartridges purchased though the DSG.