First of all, welcome to the forums.
For the places who sell HAM/radio supplies, as others have mentioned Katranji (or
EKT ) is a possibility and
RS-Online is an outlet to buy stuff from the UK (mind you they are pricey). RadioShack definitely closed all over Lebanon a while ago.
Now for electronics and parts, you might find what you need at
Incotel on Doura, same for Boujikian Electronics. There's also Kubi Electronics but it's deep into Burj Brajneh so I wouldn't venture into the area on my own (you can take the Sawi bus number 12 to end of station and walk all the way to Arab Mosque; that's what I do to get there). Kanafani is also an option, but usually his products are a bit old so you might wanna watch out for that.