Maybe you should combine all the 500 file into one files and add an additional column called "symbol" to indicate the stock symbol (or even company name if you like). This can be done very easy either by program or by some software.
And then maybe you can have a filter based on the symbol to do your analysis like the following screenshot.
Have you thought of any integrations tools before connecting to Tableau? Alteryx?
You can refer to the below thread and should be similar to .csv
No manual data preparation nor an external tool is likely necessary for this task.
1) Use Tableau's wildcard union feature to load in all the CSV files at once. Union Your Data - Tableau
2) If some fields have different names in separate files then you can use the Merge mismatched fields feature (see the documentation link above)
3) You'll want a column for the stock symbol or company name. If that's already in the file, then great. If it's not in the file but is part of the file name, you're in luck because Tableau automatically makes the filename a field in unioned sources. If necessary you can parse out the symbol or company name using a calculated field or Tableau's Split feature. Split a Field into Multiple Fields - Tableau
4) Then when you build a view all you need to do is drag the stock symbol/company name field into the view as a dimension (pill which it will most likely be categorized as the first place).