You can get Elekid very early in White 2, but you're gonna have to trade to get Electivire anyway. However, Heracross is exclusive to Black 2. So in either case, trading is necessary unless you hack. Also, check Bulbapedia and Serebii before you ask questions like this. I understand you want straight answers, but you avoid can the storm of crap that you'd have to go through to get information from a forum like this if you just took a little time to search yourself.
I actually checked both Serebii and Bulbapedia, they were both very vague about it as well, and I checked /vp/. I've done some research... --- So I'm still waiting for Daisy to reappear in something that's not a spinoff. I'll probably end up dying first or something but optimism is fun.
Where's Serebii himself when you need him? We need a Serebii-Signal. --- Yog-Sothoth knows the gate. Yog-Sothoth is the gate. Yog-Sothoth is the key and guardian of the gate. Past, present, future, all are one in Yog-Sothoth.
Heracross is predominantly exclusive to Black 2, as seen in our exclusive list. However, it IS accessible within White 2 in the Pinwheel Forest Interior Hidden Hollow. It has a 0.25% chance of appearing --- Serebii from the amazing Serebii.net Your #1 Source for ALL Pokémon Games & Anime info as the top online Pokédex & Attackdex!