Welcome to the Q&A Forum

It is like to find an ad agency - you have to ask yourself e. g.:

• Where am I or the targeted market oriented? (Do you want a company from different city/state/country/continent?)
• What is my budget? (Some SEO agencies are focused on small budgets, some on enterprise level.)
• What kind of work or cooperation I am looking for? (Some agencies are experts in link-building, some in information architecture, some can offer everything on very high level.).

You can try http://www.sempo.org/?page=member_directory but it is not useful in all countries nor some good SEO companies are not participating.

Another resource is http://www.topseos.com/search-engine-marketing-companies/seo/, but less reputable.

You can find some SEO experts even here: http://www.seomoz.org/users and http://www.seomoz.org/marketplace/companies..

My best advice is to send press releases in HTML with appropriate links.

Many journalists work in a style "receiving press release -> CTRL + C -> CTRL + V -> making some small changes -> publishing."

The old-style PR workers send just press releases in MS Word. The new style is to send both MS Word and HTML. The journalist just copies the pure and perfectly coded HTML file into their CMS and publish them. The journalist save a lot of time by coding and you get the point.