I haven't used SFS for some time, but as I recall, there is an airfield
that you can select as your start point where the launch is aerotow
(most of them are winch).

There are some 3rd-party add-on gliders and motorgliders available for
Microsoft Flt Sim - and there is a website with downloadable thermal
scenery, but sorry, I don't have that link info handy...