You should be able to get the glue from most automotive shops (scotties, supercheap repco etc). Your best bet would to pay a visit to the 3M website and find a local authorised dealer, if your local authorised dealer dosen't stock it they should be able to order it in for you. The spray comes in an aerosol can and the part number is #08088
I not sure of cost but I think it is around $20 in NSW might be different in other states.
Another glue you could use is GPI brushable glue it is in a black can. It is good for doing jobs where you need complete glue coverage not just spray lines.
Either glue will the job. Personally I would go for the GPI glue if I were doing a roof lining but for door trim I would use either.
If you can't find either glue maybe we can sort something out as I can get bothe glue types.
Depending where you live AUTOWEST PAINT SUPPLIES have a delivery service that goes to Windsor and surrounds, granville, arndell park, blacktown,minto,bathurst,orange,smeaton grange,silverdale,seven hills.
Theey can be contacted on 4721 3301