I think the best option will be to build out your own in-law suite by converting a basement or attic space, or putting an addition onto a home (in law wing with separate entrance). It will give you more options.
Another option would be to consider a 2 family and there are currently 3 on the market right around your price range. Click this link to see them all with a map:
The only single family property coming up using the key word "in law" is the below. Looks like a complete gut renovation (but a nice lot). Chances are you will need to pay all cash (or put more than 20% down). I cant imagine you can get traditional financing for this project.
Here is every property on the market in North Attleboro: