When are your dates of travel? Looking at Delta, they only fly to SXM from ATL. There are connections on either end that are manageable for this summer: a 705a departure from RIC that arrives in SXM at 207p (1h09 in ATL) and on return, a 320p departure from SXM that gets into RIC at 1116p (1h46 in ATL, and you need to clear customs/immigration).
AA also has easy connections - Lv RIC at 720a, arrive SXM at 215p (1h30 in MIA); Return at 325p and get into RIC at 1140p (2h40 layover in MIA).