Your company has made the decision to pursue non-dilutive funding. Locating agencies and choosing proposal topics is an important first step down the road to winning SBIR funding.
I group solicitations into two buckets: investigator-initiated, and agency-initiated. For example, NIH has both, NSF solicitations are agency-initiated but are broad topics, and DoD are strictly defined agency-initiated contracts.
Here are some resources that can assist you in identifying solicitations.