I don't want to be in a position of saying the film suffered because it lacked my personal involvement because that was definitely not ever my intent. I know that was not your intent either. I bring this up because if you read Mark Bando's Trigger Time website, his critique of Band of Brothers is filled with bitter recriminations. I sympathize with him; he is a pre-eminent historian of the 101st Airborne Division, and he was not consulted for the project. However, his critique of the miniseries is so in-depth (read: nitpicky) and his comments are so bitter, that if I were a film maker, I would never in a million years hire him as a consultant. And I've said as much on "to his face", or at least on his own web forum. I do not want to be seen, therefore, as pouring forth sour grapes myself lest I acquire the same reputation.
And I don't think anyone else is here, either. I am glad you bring the subject up, and especially your own research regarding the Regina Rifles. A film like this has the real ability to reach out and renew interest, as you point out. I personally believe Saving Private Ryan renewed interest in the Second World War throughout the English speaking world to a major degree - and the ramifications of that film are still with us today. I'd be willing to say that if SPR had never been released to such critical and commercial success, we would not be seeing projects like BoB or indeed Storming Juno, as there would be no perceived market for them.
With all those caveats out of the way, I do agree that the "community" has much to offer. I know that at least half a dozen of the participants in this thread alone have loaned kit and expertise to past film projects. Many do so without recompense; I have certainly done so. I don't think money is the issue. I would have been thrilled to send out a set of rifle regiment insignia for inspection to the film-makers so they could replicate same. Or read the script over to suggest period radio dialogue or slang. I do think that time was the great conspirator, and of course, a movie is a collaborative project, meaning you have dozens of people with conflicting schedules and objectives - often meaning that not everything you wish to accomplish can indeed get done.
There has been talk in the past about 'central registries' of historical resources for film-makers, and I think Harlan Glenn in the States (I think) even set up a business with an aim to supplying film-makers with appropriate resources for British Commonwealth themed movies and TV projects. It was a for-profit venture, but as you point out, a couple of emails would have yielded some interested advisors for gratis. That pre-supposes they needed a lot of long-distance advisors with no way of rendering tangible assistance on-set, or that even if someone could have been there, the timetables permitted any real changes on the advice of such an advisor. It may be that they had all the advice they need but were simply unable to act on it. I've been in that position before; the Heroes of the Victoria Cross producers asked me several times about certain details of uniform, for example, and after sending several diagrams and even examples of patches as worn at Dieppe, they still got the wrong ones on camera. Whoever was in research just didn't have the juice to get the costumer to use the right ones. And I'm sure the director had 3,000 other things to worry about and was oblivious to the whole question.
I think as a community, the best thing we can do is stay open to providing support to productions like this, offer assistance where possible, and accept that it won't always be possible for them to accept it.