http://www.Realtor.com is the site you need to use if you want to easily find the Listing Agent as you search for property.
MLS Data Accuracy â€“ Where to search if youâ€™re â€œwithout RealtorÂ®â€
However, what you seem to be wanting is a "Dual Agency" for some reason. There are specific duties an Agent must provide. When one individual represents both Buyer and Seller conflict between two of the most important duties occur.