Does anyone know how to find the fiat value of a transaction at the time it was received using a block explorer?
Use
blockchair.com. It shows the value of inputs and outputs at the time the transaction was made.
Look at the image below. It's a random transaction made in September 2012. As you see, it's showing only 126 dollars for 10 BTC.
blockchair.comAlso, does anyone know an easy way to scrape the transaction data from a bitcoin address directly into a spreadsheet?
Create a watch-only wallet on electrum. Click on "wallet" at top of the window. Select "History" and then "Export".
For selecting the fiat currency, click on "Tools" and go to "Preferences".