Captive boa constrictors do not have a set breeding season unless you artificially create one for them.
Female boas are ready for breeding shortly after they start forming ova. The hormones that start the process of developing ova will also give off a smell to attract the males. Males will not mate unless the female has started the process of developing ova and smell right.
The goal then is to stimulate your female to start the ova forming process. There are three ways to do this and I'll talk about two of them. The first way to do this is to give them a seasonal temperature drop. Adult females with good healthy body weight will often begin forming ova if given a drop of temperature in the fall/winter. A drop to 73-76 degrees at night and then raised to 83 degrees in the day is about perfect. This seasonal drop of temps will do you no good however if your female is not fully mature and does not have adequate fat reserves to develop ova. Ova is made of mostly fat so your boa will need to have good weight.
The second way is called the fat/ovulation cycle. Fully mature and healthy females can be put on 3 to 5 month program of feeding on double the amount of food you would give them during normal maintenance feedings. The goal here is to increase the body weight by 25%-30% by the end of this 5 month "cycle." Many adult females will naturally convert this extra body mass into ova......and therefore are ready for a male
Boas are really much easier to breed than many think.
A word to breeders about ovulation: Many people believe that when a female is pushing the ova to the waiting sperm she is "ovulating" but this is not true. You have all seen this in person or in photos...a large football shaped swelling that can last up to 24 hours and sometimes happen twice. But this is really just the final step in the ovulation process. Ovulation is taking place from moment your female begins forming tiny ova follicles until she pushes the fully developed ova to the waiting sperm. Once contact is made with sperm the ovulation process ends and she is now gravid.
There...now you know how to breed boas...well mostly