Not sure is this is the best place for this. I have been designing a role-playing system this year and my primary goal is to be historically accurate when possible. While I can find lengths for weapons, its rare that I find a weight. And with armor, its even harder to do. Is there a source that someone can suggest? I have guessed at rough square footage and used a per square foot weight for steel and other materials. This has been surprisingly accurate based on the limited weights I have been able to find, Since I do not have, nor can afford to buy an example of every piece of armor, this has been a real challenge. I find it hard to believe no historian has sat down and measured and weighed various armor pieces and published the result. I realize not every piece of armor is available, but surely there are similar examples that I could at least make an educated guess? I have used replicas for weapon sizes, but even they rarely list weights. My biggest challenge is helmets. Any help would be appreciated and could be credited.

A good place to start is to trawl through the online catalogues of major arms and armour collections. For example, the John Woodman Higgins collection. https://www.worcesterart.org/collection/higgins-collection/ or the Royal Armouries https://collections.royalarmouries.org/#/objects (in the latter case, use the object data tab, which often has dimension data). There are many others with catalogues on line .

Get a hold of GURPS Low-Tech.

The Wallace Collection is also a great resource. I made a spreadsheet of weights, lengths, year, potential maker, balance point when available of longswords and arming swords from that resource. Because I'm a huge nerd.

https://wallacelive.wallacecollection.org/eMP/eMuseumPlus

Just use the dropdown menu for arms and armor.