I understand Zhuge Liang and Cao Cao wrote books and other material attributed to them, but are there things like seals of their office, or any tangible pieces of art from that time which mention the kingdoms and their leading figures?
How soon after the deaths of Guan Yu and Zhang Fei were temples erected to them?
(I'm not skeptical of their existence even though this question probably sounds like that, just interested in archaeology of the period)
The most note able book was Records of the Three Kingdoms by Chen Shou which I assume you know about. A lot of poetry and writings exist for the time, namely Cao Cao's, Zhuge Liang's and Cao Zhi's. I don't know of any weapons or other archeological finds that contribute to a certain figure of the Three Kingdoms though I know for sure there's plenty of finds relating to the period.
Shrines erected for Guan Yu was quite a bit after the Three Kingdoms period, primarily during the Tang Dynasty a few hundred years after he was starting to be defied. Not sure about Zhang Fei.