If you reach out to them, make sure you have a pretty solid and equal arrangement between the two of you.
Have back links in the items descriptions that you collaborated in to each others stores.
Also promote the collaboration on social media by saying, "Hey, xyz store and I are collaborating on these items!"
Make the collaboration seem well worth it to the other person. Tell them that you have xx amount of followers on Etsy (plus any social media), that you intend to let people know about the collaboration, your marketing campaign, etc. Its nice to know that someone would want to collaborate, but theyll also want to know its worth their while to make the said products.