All three players will now call Punt Road home until the end of the 2023 season, inking new two-year deals.
“Kamdyn and Jason have been outstanding contributors for us across the journey, particularly as regular members in the senior team the past five years,” Tigers' general manager of football talent Blair Hartley said, per the club's website.
“Both add specific skill sets that are important to the way we play and are excellent trainers and characters to have around the group.
“Thomson has worked hard across his first two years at the Club and has shown plenty of upside despite the interruptions he has faced. He is a player that we are really excited about.
“We are thrilled to have Jason, Kamdyn and Thomson sign on and look forward to seeing more of them across the next two years.”
Castagna, a three-time premiership player with the Tigers, has been a key asset for the club in their recent success, booting 114 goals for the club since making his debut in 2016.
The 25-year-old has played 117 games across his seven seasons in the yellow and black.
McIntosh, a two-time champion with Richmond, has flourished in a new role further up the ground this season, having a larger impact on Damien Hardwick's attack from the wing.
The 27-year-old has played 124 games for the Tigers since making his debut with the club in 2015.
Dow, despite just the six games to his name, has shown great promise in the early stages of his career.
The teenager has played four matches for the Tigers this season after making his debut in Round 14, 2020.