Try e-gunparts.com
80-125 USD
25-50 USD
The one that came with it
Try gun shops, gun shows, want ads.
It should be marked on the slide. 22LR (.22 Long Rifle)
Want ads, gun shops, gun shows, e-gunparts.com
I have one which was purchased in July 1980 - it just has 'Singer' on it, but I've just seen the same one sold in New Zealand on an eBay type site and it has 'Merritt' on it.
If attempting to purchase the organ the value is the amount that you are willing to pay. If selling the organ the value is the amount that you will accept and the buyer will pay. It is hard to put a price on such a great item that will provide one with numerous memories that money simply cannot buy.
Enfield L85A1 or A2 hard to tell for sure without a closer look but it's one variant or another of the SA80 bullpup design by Enfield except for the L98 (no flash supressor and clearly the rifles they carry have one) or the L22 carbien.
Lorcin L22s are junk. The build quality is inconsistent to the point where the ideal ammo for one gun may be problematic for another. You'll have to experiment with various types of ammo to find the ideal type for your pistol. Remington Subsonic may be a good place to start.
For a sidearm they use the Browning Hi-Power pistol. for their main fire arm they use a L22 A2 assault rifle. this is a shorter version of the L85 A2 assault rifle(SA80). it can also be called the L85 carbine.