Floor registers get expensive. They are heaver gauge metal.
Personally your going to do a lot of work for very little gain other than appearances.
I have had good luck with this company in the past.
Atlanta Supply is the largest distributor of HVAC vents, registers, and returns in the US. Choose from more than 6000 sizes and styles we have available!www.atlantasupply.com
Many shared wall registers were designed for gravity heat with no fan and don't work well on forced air setups especially for cooling.