I would like to start a console window which invokes bash and have bash execute a bash command ( 'source' ) and then remain open for further user input ( be interactive ). I imagine this must be possible. How would I do this ?

I know I can add the command to ~/.bashrc but I do not want to have the command execute each time I run a script, but only during a particular console session.

I can tell you how I would do this then you will probably have someone tell you a better way.
First create a special profile terminal. Do this by opening "gnome-terminal". Right click inside the terminal. Click "Profiles" then "Profile Preferences". Under the tab "General" the top line "Profile name" change it to whatever you wish to name it. Then click the tab "Title and Command". You might want to change the "Initial Title" to the Terminal Profile Name you chose before. Then down at the bottom where it says "When command exits" change that from "Exit the terminal" to "Hold the terminal open". Now make an icon with your menu editor under, say, utilities. Name it whatever you want. Click in the box on the right side "Command". Type "gnome-terminal --window-with-profile=profile_name -e some_command" where "some_command" is the name of your bash script you have written, placed somewhere in your path and done "chmod +x some_command" to make your script executable. The script will run and the terminal will remain open. Oh, and check the box "Only show in KDE" if you're using KDE. The top right box, you can click on that and choose an icon. Good luck.

I am using Konsole under KDE and unfortunately there is no "Hold the terminal open" for Konsole profiles that I can see.