You should click "Free" option.... then enter code from picture and download...
EDIT: If You can't obtain m82 You can use spawner mod. Add entry properly to ui_si.script
"wpn_m82",
EDIT2: Could You also tell me what entries I should edit for handling, accury, damage etc?
[Edited by Bali-X, 10/25/2009 2:25:13 PM]
Explained here for weapon accuracy.
forums.filefront.com/s-t-l-k-e-r-soc-modding-mapping-editing/369316-editing-weapon-accuracy.html