You can always go to public weigh-ins, press conferences, training days etc. Going to gyms is also feasible; I've seen both Arnie and Billy Nelson say their gyms are open to anyone from here that wants to go.
As for contacting fighters/trainers, you could always use Twitter. As a matter of fact, I recently seen Kevin Mitchell signing gloves for people that asked on there. Frankie Gavin in the past also offered anyone on here a signed glove if they wanted one.
We're lucky because boxing figures are so accessible, so you really shouldn't have a problem getting some signed stuff