You can send Kontakt’s script generated notes out the Kontakt block’s MIDI out.
1 - Set up a Kontakt instrument and go into Script Editor - Preset, Factory, Harmonize, Interval Tonal, and adjust the settings as desired.
2 - Then choose OPTIONS, ENGINE, SEND MIDI TO OUTSIDE WORLD, SCRIPT GENERATED NOTES.
3 - Connect the MIDI out block to your RealStrat input (along with your regular MIDI input), and the script generated 3rds will play with you in real time.
(It doesn’t matter what instrument you choose in Kontakt, just don’t hook up the audio from Kontakt, use only the MIDI out)