Cover letter help

[Amy]

I'm running around like a chicken with its head cut off trying to find a job here. I've applied for a 2 semester post baccalaureate paralegal certificate program through Texas State and am waiting to hear back. My first step here is to apply for an administrative position at various law firms in town- the hours are going to be better than any service-related jobs (restaurants, retail, etc) which are going to probably require weekends and evenings. However, I don't know how to tailor my cover letter, since I'm basically going to be bringing it and my resume in to every family law firm in town (I haven't seen any job postings online). The only way I've ever seen to write a cover letter is to start with an intro paragraph about how you came across the job ad- I don't know how to do this. I've also heard not to address it "To whom it may concern"- I'm not sure what to do about this, either. I suppose I can call every one and see who is in charge of hiring decisions?

Anyway, any input would be appreciated. I haven't looked for a job in years, haven't worked since my daughter was born, and I'm scared I'll never find one.