1/2" Type K has an ID of 0.527", which works well for sliding over FL-524, but is usually not carried in home centers. McMaster-Carr has it in a couple different lengths.
1/2" Type M & L can usually be found in stores, and can be used with connectors where it's not being placed over the core (in a 45 deg pistol grip pommel, etc). All types can use the same 1/2" connectors, as the outside diameter (5/8") is the same for all of them.
Copper sections & connectors can be "sweated" (soldered) onto each other with plumbing supplies (flux, solder, and a torch), or a sufficiently powerful enough heat gun.