There usually is an hospitality tent type thing towards the rear left of the stage where the band and otherr guests meet up after the gig. Unfortunately, the place is guarded and without a pass you wont get anywhere near it. Likewise with the tour bus, this will be parked in a fenced off area at the rear of the venue and too is guarded to an extent, but you might be able to get through
I would recommend you get in touch the venue management and put this request through to them and/or contact the Quo's management team and see if something can be arranged that way. I'm sure they would sign something, maybe not on the night, but it's better than nothing I suppose.