Help with a custom search filter

Hi, lads.

I'm building this site where i have different stores with different products each... my client wants a couple of things and I don't know hot to do them,

1- He wants a custom search dropdown filter in each product page, so the client can filter by zone, to know wich is the nearer store where that product is available. I thought I could create custom taxonomys in the product and there add tags for each store where that product can be found... the thing is that there are a lot of stores trough all the country, so I just can't display all the tags, I nee to create a dropdown filter to filter the store by state and city... I think I also need to categorize each store with their location (state, city), but I don't know how to create that drop down filter in each product page, who searchs trough teir own store tags and filter the results of the location categorys of the store...

Please, please, can you help me?