I've just found a source for Thunderbolt Roots blowers that also use the same type & size of this blower.
The type of equipment that uses this blower is known as truck mounted carpet cleaning equipment. In fact,I once saw in person this type of equipment using the same blower that have the same threaded blower outlet & inlet connections the T-bolt blowers use. Also,the T-Bolt roots blower of the same kind is used on vacuum tank trucks,the kind used for cleaning grease traps,grease containers you usually see at restaurants,portable toilets,etc. If you do need a T-Bolt blower,search the forums online for these equipment types that use these blowers & explain specifically what you need a Roots blower for which I did already.