(optional, highly suggest) ModLoader
(2.)How to do it:
"Guns on LS-RP are hard to get", yes if you try to get them the normal way. But, with only one weapon mod, you'll easily find guns that are hidden in the cars, or on the ground by any chances.
First off, you need a weapon mod for a weapon that is huge. By that I mean very very big weapon mods. I have left a link of the weapon mod I use below. I'd also highly recommend that you install the weapon mods with ModLoader, because you'll easily be able to remove that mod after you're done gathering your "straps".
Secondly, When you download the mod, rename the "gun_dildo1.dff" to the gun that you want, ex. "desert_eagle.dff", "m4.dff"...
Thirdly, when you install the weapon mod, simply get into LS-RP, and search walk around cars. If there's a weapon in it, you'll easily be able to spot it, because of the huge weapon mod. When you find one, break into the car, hotwire it, and /takegun.
(3.)How NOT to get banned:
1. Try not to make it obvious that you have a mod. Don't walk around the cars, and suddenly say "oh I'll jack this one". Pretend that you're trying to jack some other cars before the one where the weapon is.
2. If you see someone driving a car with a weapon inside of it, don't follow them. Or try to follow them, but remain unspotted by the driver.
-The weapon mod I use: http://www.gtanetwork.it/zone/pafiledb.php?action=file&id=5823 (don't replace the melee.dat file)
This is a very simple trick I used. It might take time to find a car with weapons inside of it, but, after a while you'll find one.