Okay, I can help you with this. I manage a county child support office in Minnesota (please, do not hate those of us who do this work for a living. It is more complex than you can imagine and most who commit to it as a career do so because we sincerely care about your kids and feel passionate that both parents should support their children. Sometimes we can't help it that your ex is a loser). In the 17 years I have worked in child support, I have NEVER met a private attorney who knows two hoots about interstate child support law. But, if you decide to go that route, I would hire an atty in the state your ex lives and have him register your MA court order for enforcement under UIFSA (Uniform Interstate Family Support Act), the federal act adopted by all states as law to deal with interstate child support legal issues. The atty could then file contempt charges against your ex in MA. It will likely cost a bundle.
I personally think that having your local child support office assist you is your best and least costly alternative, but as I can tell by reading this thread, many here view me and those of us who do this work as the enemy so it's up to you. Do you currently have an open child support case in MA ?(that you opened before you moved to FL and failed to close?) Your answer to that question would direct what steps I would tell you to do next. If you want to PM me instead of post publicly, feel free. I am happy to help in any way I can!!