Arthur - I do not believe you will find a provider that will deliver SIP as a usable DID trunk that the PBX can use. I would advise reaching out to a company called Multitech. They make a SIP to FXS gateway that does have the ability for the customer side to be configured as DID trunks.
What you might be able to do is get the SIP Service with a block of DID numbers and have this gateway do the necessary conversions. You can also configure standard POTS ports so outbound calls can be placed on the service as well.
We have not done your scenario exactly but I have used Multitech to extend service to remote areas that have network connection to a main site. The remote was connected across a busy street to a main site with a wireless bridge. They wanted paging and fax machines at the remote site but did not want to pay a monthly fee for dial tone so we used these gateways to extend analog station ports from the PBX to across the street.
This application has been in play for a few years so I can say the equipment is well built, reliable, and that Multitech is very responsive to helping us configure new applications and maintain existing ones.https://www.multitech.com
Data sheet on the gateway:https://www.multitech.com/datasheets/86002027.pdf