There isn't anywhere that is totally accurate. Amalgamating Google and Bing along with a social scrape (essp for B2C niches) will give you the best idea.
Scrape Google
Scrape Bing
use a social site like hashtagify to get a third opinion.
Take a mean average.
The real win is experimentation. With the best data you can gather perhaps try a tiny adwords campaign. Funny how once you do that and put the Google keyword planner into a real adwords campaign the enormity of just how shit the keyword planner is can sometimes be shown.
Bid - $1.20 in Keyword planner
Bid that in a real campaign and be hit with "Your bid is below the first page value, Expected bid $3.86"
The old "bait and switch" get you hooked with a low price, then once your customer is emotionally invested in the project - triple it.
