Ever since I moved f to the Pacific Northwest I have had trouble finding mantids too. I've only seen one adult male and a few oothecae. There are a couple of species that could be in your area. 1. Mantis religiosa more commonly known as the European mantis. These look like your common mantis being green, straw, or brown in coloration with an eyespot-like shape on the inside of their front legs. I most commonly see this species as adults or large nymphs in late summer through fall, mostly in places with lots of tall grass such as fields. I've seen their oothecae on man-made surfaces such as fences or under windowsill ledges, or less commonly under logs or on grass. 2. Litaneutria skinneri, this is a species of small ground-dwelling mantis. these are much smaller than the European mantis and are usually a mottled brown or grey in coloration. this species is very small and easy to overlook. I have only seen these on a few occasions on rocky or gravelly ground with little vegetation except for some short, dry grasses. I have not l seen any oothecae of this species. There are a couple of other mantises that live in Utah in the genus Stagmomantis but they mostly live further south.
I hope this information can be of some use to you or anyone else who may struggle finding mantids.