I will occasionally update this post with with new sources. If you know of one not listed below please reply below and I will update.
Allen's Fasteners
Altha Fastener
AMK Products (Author of AMK Products Guide to Ford Fasteners 1957-73.)
Auto Fastco (The Fastener Warehouse)
Auto Krafters (Print catalog may have parts not reflected on website - just call them and they will quickly get it added
.)Auto Parts Obsolete
Auveco Products
Car Parts Discount
CJ Pony Parts
Clips & Fasteners Inc
Classic Car Auto Parts (aka Obsolete & Classic Auto Parts) (Limited selection, mostly NOS parts)
Classic Industries (Including 13190 Seat Track Mounting Plates.)
Classic Auto Supply Company (Including 356383-S Spring/Multiple Wave Washer.)
C&G Ford Parts
Dennis Carpenter (Website is horrid - start with their 1960-70 Falcon Catalog.)
Dearborn Classics (Click on either "Interior Parts and Trim" or "Exterior Parts and Trim".)
Döttling Ford Thunderbird and Falcon Connection (They have a Comet section but the Falcon one has way more parts... so check both.)
Ebay Vintage Parts for 1965 Mercury Comet
FalconParts.com
Hilco Fastener Warehouse
John's Mustang
Kentucky Mustang (I think they have, literally, every part for a 65 Mustang.)
Larry's Thunderbird & Mustang Parts (Ditto.)
Lincoln Mercury Old Parts Store
MACs Auto Parts
Mustang Depot
National Parts Depot
NOS Parts Ltd.
Melvin's Classic Ford Parts (Must omit hyphens in part number searches!)
Mr. G's Enterprises
Mustang Project Custom Car LED Lighting
Obsolete Reliable Parts
Original Falcon Interiors (Dealer for SMS Auto Fabrics - see below.)
PG Classic Restoration Parts LTD
Rear Counter (NOS parts can sometimes be found here that are not already listed on ebay)
Restoration Parts Source (At first glance the Comet selection seems kind of lame however with a bit more digging you'll find that their Mustang selection has many overlapping parts that have not been tagged to appear under Comet.)
Restoration Specialties
RockAuto
Rubber The Right Way
Scott Drake
SMS Auto Fabrics (Super detailed - their site even allows you to select your factory trim code from a drop down - super cool!)
Steele Rubber Products
StangerSite Everything steering, power and manual.
Summit Racing
SuperBrightLEDs.com (Impressively accurate catalog of every bulb that appeared on Comets, however as of March 2020 there is a poor recommendation for the blue instrument cluster cans - their recommended blub is too long - when installed the bulbs have a a tendency to push against the blue cans such that they are pushed back into the receptacle thus disconnecting from their ground (sometimes even causing a short).)
Vegas Rod Parts (Custom manufacturing the '65 Grill as a reproduction part.)
Virginia Classic Mustang
W&E Sales Co., Inc.
YnZ Yesterday's Parts (Especially valuable selection of electrical terminals sold individually!)
