That's why I asked what powders you actually HAVE. There are many many powders for 38 special and 357 Mag.
If you can not find data for a 100 gr bullet you can use data for the next higher weight bullet such as 110 gr.
Trail Boss can be calculated using the information found here in the upper written part.
Click on
Data and pull down the Trail Boss Reduced load data and follow the instructions.
Hodgdon - The Gun Powder People
I would have to look in my manuals like Lyman CAST to see if they have a 100 gr bullet. That is a odd weight?
Bullseye is a fine powder for the 38 special so you do not need another one. The question is the load for that small bullet. I know what I would use but I am not posting load data. I would not shoot it in 357 Mag.
You can look here and develop your own.
Reloading The .38 Special Page