Can one put a sep. funnel(filled with drying agent) that has ground glass, on top of the condenser for dry reflux.

It is not a good solution, as the sep funnel valve is so narrow, it could spell disaster if you for any reason would get overpressure inside the reaction setup (the sepfunnel would fall off).

If you decide to use this setup anyway, make sure that you put some kind of filter (i. e. steel wool) at the bottom of the sepfunnel to prevent the drying agent to fall into the rxn mixture.

Perhaps an addition funnel would be more suitable, and less ghetto :-). Addition funnels tend not to have a skinny stem that is typical in sep funnels.

I can't find a drying tube anywhere, any suggestions?

Take a regular bent vacuum adaptor for the reciever end of a still, stuff a lil cotton in the drip tube(from the condenser opening, don't stuff it just lay over top of hole to stop dessicant) and pour in some dessicant. Plug with cotton or glass wool. Ghetto drying tube with ground joint, viola.

Edit: Oh yea, you'll need to stick a piece of something in the vacuum takeoff nipple. I just ball up some teflon tape like a little joint. The thick center will stop it going all the way in and make a tight seal.

https://www.thevespiary.org/rhodium/Rhodium/chemistry/equipment/inline.gas.dryer.html