Where is the best place to find one or who sells one for a lvl 100 glalil or weavile

You should check the trades section of the server you're playing on, you could also try asking in the trade channel in-game in terms of best place to hunt for one I suggest surfing on route 24 as if you surf the only two Pokemon that can spawn are Goldeen and Krabby making it very easy to find a h.a Goldeen, additionally I'd suggest taking a Pokemon that knows thunderbolt and simply use it against all Pokemon you find until you find a Goldeen that absorbs it which will then have Lighting Rod.

Hope this helps.

Go surf in Tohjo Falls (cave between Kanto & Johto) it only spawns goldeen and seakings so getting a lighting rod one is very easy, bring a modest Kadabra/Alakazam with Roleplay and it will go really fast.