I tried to find info on how I ask a provider for a referral, but can't find anything.  I just saw a provider for first time in a few years as I'm just getting back in the hobby.  As such, I'd like to ask for a referral so agencies and other providers at least have that for authentications.  Thanks.

ask the provider you saw if it's okay to use her name as a reference. you don't have to do this, but it's considered polite.
then, when you are asked for a reference by another provider or agency, just give them the name and contact information (including reviews or website) of the provider you saw, as well as something to trigger her memory of you... perhaps something special you talked about or an interesting gift you gave her. even when and where you saw her can be helpful.