Not entirely sure how the version the Lithuanians are buying differs from regular g36k's, most images available seem to show a variety of variants, longer/shorter barrels, subtle differences in the foregrips etc ?, But nothing that screams "Lithuanian variant".
Might help if you can post an image up of what your looking for, & hilight any known differences ?
I actually doubt there is an out of the box Lithuanian G36. Though as long as you can find the specific RIS front set you want, you should be able to build it from either a G36E or G36K.
A lot of the pics I can see seem to actually be a barrel length between a G36E and G36K with a K length RIS unit (and a lot of bare barrel up front). So you could get yourself either, replace the optic with a G36C rail up top and the RIS unit up front.
These might be okay base guns as they already has the rail up top and you would only need to source the RIS front set: