If you have a decent Z-Wave mesh (with powered devices that repeat) you might want to take a look at these sensors - GoControl 5 Pack for $50. Others have used these successfully with Hubitat.
If you prefer Zigbee, there are lots of options.
If you act quickly, you can still buy some Iris sensors at Amazon.
Almost all Iris v2 devices were made by Centralite.
You could try these sensors.
https://store.centralite.com/products/3-series-micro-door-sensor
Some folks use SmartThings sensors (not sure if Hubitat support all of the features of the following sensor yet.)
EDIT: Per @mike.maxwell - this one may be a better/newer choice
https://www.amazon.com/Samsung-SmartThings-Multipurpose-Sensor-GP-U999SJVLAAA/dp/B07F956F3B/ref=sr_1_2?ie=UTF8&qid=1549126883&sr=8-2&keywords=samsung+multipurpose+sensor
Others have mixed success with the very inexpensive Visonic sensors
However, I will caution you to steer clear of Xiaomi sensors. The are not 100% Zigbee HA 1.2 compliant devices. You will have to tinker quite a bit to make them work reliably. If you have Irisi 3210-L outlets, the Xiaomi devices are know to be incompatible.
