You'll be surprised because thankfully the Violent Crimes Reduction Act grandfathers replicas bought before the 2007 date. Maybe someone you know owns a few and will lend them to you for the duration of your film shoot.
Since film making was stated in the Act as an exemption you could always test your creative side and make replicas out of cardboard or wood. Print a 1:1 scale picture of a gun then use that as a template. You can probably make a few in a day and they should look okay on camera. Unless you're good at arts and craft chances are your gun wont look that realistic up close so try and be clever when you use this method. Have quick camera shots of your actor shooting and hopefully your audience wont notice it's a lump of cardboard.
Maybe if you're a wizz at computers you can film your actors "pretending" to hold guns and then create a 3D model on the computer where the firearm should be. Chances are it'll look too fake but it might be worth a shot (sorry, bad pun).
Buy what you can:
Good news is you can still buy non-realistic replicas. These are basically the exact same size but they come in bright happy colours like green, blue and orange. You'll ask "But how can these pass as real on camera??". Well, most editing software has a colour key effect which you can apply to your video clips. Say you've got a bright orange gun and you've just shot an action scene you apply the colour key filter then select orange for removal. And depending on your software, you should be able to desaturate and adjust brightness on the orange areas so the gun then becomes black. This method might be the most cost effective way of putting prop guns into your films. Search for cheap BB guns online and you can buy accurate replicas of modern firearms in bright colours. http://www.justbbguns.co.uk/ is a good place to purchase from.
Also, replicas based on a design from before 1870 (not 1970) are allowed to be purchased by anyone which is good news if your film's going to be a western.
Become an air-softer:
Alternatively, join an Airsoft skirmishing site and by running around a forest and getting dirty for a few times a year you'll qualify for VCRA exemption! This means you can purchase as many realistic replicas as you want.
Start a Film Company:
If you don't want to run around a forest and get dirty a few times a year then consider setting yourself up as a film company. This really only makes logical sense if you're serious about filmmaking (Like me). Set up a business account with your bank then visit http://www.companieshouse.gov.uk/ to register your company. Hire some friends as employees then fill out the necessary paperwork and so on. You might need public liability insurance though so do your research and ask around first. Once you get past the headache of setting up a business you can purchase replica guns online. I suggest buying off http://www.plugfirecapgunsuk.com/ because they stock a large range of blank firing replicas which provide extra realism on set.
(Pictures coming soon)
And now for a bit of advice. If you use anything that looks like a firearm please don't wave it around in public and ensure that everyone around you knows that it's a fake gun. Next post I make will be a tutorial showing you how to add gun effects like smoke, muzzle flashes and shell casings to enhance your action scenes.