Google is your friend. When I'm, researching I start with a basic search like "Beck's IBUs" Then I look the brewery website, most micro and a few macro breweries put all that info and even their complete grainbills or recipes in percentages right on their website. I also search for clone recipes online as well, they usually will be going by that info to create their clones, and may even mention or list the original beer's info, but if I find multiple clones and they all are hitting the same IBU's or og or srm, then I figure they had that info.
Also obviously the bjcp style guidlines will usually have the range of numbers for that particular style, and will list commercial examples of the beers, so you again will be in the ballpark