Best way to get a list of businesses in a specific area

[Hoofy]

Want to target companies with 50+ employees. I could buy the list but I don't want 1000+. I just need maybe 20-30 that I can investigate before approaching. I suppose I could use Google Maps and look for business names in various business parks but is there a smarter way of doing this?

[Hoofy]

Thanks. Just had a look. Right now I don't want to spend £25 a month.

[Hoofy]

Can't help thinking they'd charge. I just wonder if the info is online somehow. I suppose another way is if I find a company how can I check how big they are in terms of employee size at a given site?