You can call the listing agent and see if they would arrange to open the house for you, or you can work with a local realtor on a referral basis to show houses in the local area, or as you know, you can join the local Association to have access yourself while you are showing properties in Sacramento.
I have the same situation for another area that I am working on. Working with a local realtor will give you knowledge of the specific values in the area, as well as acccess to the homes. It all depends on how many homes you want to consider on what makes the most sense.
In addition, a licensed agent does not guarantee that the listing brokerage will pay commissions to someone outside their association area (whether you are in another association, or not). That is handled at a broker level, so even if you present an offer for your buyer, they are not obligated to compensate you.