This answer is applicable to all Mazda Miatas from 1990-2005, and it is the same factory piece across all years:
What is the moulding called?It is generally referred to as Front Beltline / Belt Line Moulding. On a Mazda Miata, it is held in by 4 plastic clips and a covered screw at each end of the moulding. How do they come off?Passenger side - NA01-58-810F
Easiest to find them at your local dealership, if you have a local Miata Club, they may have deals to get discounts. Otherwise, there are many online dealers, which are listed in the related links that have competitive prices.
how do you run the wire for the power windows on a 91 Mazda miata
The 2011 Mazda MX-5-Miata is 5 ft. 7.7 in. (67.7 in.)1 one-touch power windows wide.
The 2004 Mazda MX-5-Miata is 5 ft. 6 in. (66 in.)1 one-touch power windows wide.
The 2001 Mazda MX-5-Miata is 5 ft. 6 in. (66 in.)1 one-touch power windows wide.
The 2014 Mazda MX-5-Miata is 5 ft. 7.7 in. (67.7 in.)1 one-touch power windows wide.
The 2006 Mazda MX-5-Miata is 5 ft. 7.7 in. (67.7 in.)1 one-touch power windows wide.
The 2012 Mazda MX-5-Miata is 5 ft. 7.7 in. (67.7 in.)1 one-touch power windows wide.
The 2008 Mazda MX-5-Miata is 5 ft. 7.7 in. (67.7 in.)1 one-touch power windows wide.
The 2005 Mazda MX-5-Miata is 5 ft. 6.1 in. (66.1 in.)1 one-touch power windows wide.
The 2013 Mazda MX-5-Miata is 5 ft. 7.7 in. (67.7 in.)1 one-touch power windows wide.
The 2010 Mazda MX-5-Miata is 5 ft. 7.7 in. (67.7 in.)1 one-touch power windows wide.
The 2002 Mazda MX-5-Miata is 5 ft. 6 in. (66 in.)1 one-touch power windows wide.