If you can't get a thermostat quickly then you can pick up a lamp dimmer at a hardware store like Lowes.
https://www.lowes.com/pd/Lutron-Cred...Dimmer/3189447
Note this isn't a permanent solution but it will you dial back the heat until you can get a thermostat.
Also what size tank is your boa in and how old is your boa? You may want to go ahead and order something like a T8 now because boas get big enough to outgrow most tanks, and enclosure makers are backlogged for a few months.