2010-11: Oskar Lindblom, a native of Gavle, joined his older brother Marcus Lindblom on the hometown club Brynas' U16 team; skating in eight games as a 14-year-old. He scored 8 goals with 8 assists and had 8 penalty minutes. Playing alongside Marcus for Gastrikland in the annual TV-Pucken tournament for high school players in Sweden he scored 4 goals with 3 assists and had 2 penalty minutes in eight games.
2011-12: Lindblom played for Brynas' U18 and U16 teams. He was the second-leading scorer for Sweden's U16 team and led all goal scorers in the TV-Pucken tournament. He scored 12 goals with 14 assists in 20 regular season games for the Brynas U18 team and was +15 with 8 penalty minutes. In one playoff game he had an assist. Named captain of the Brynas U16 team he scored 11 goals with 8 assists and was +8 with 2 penalty minutes in eight U16 games. Lindblom scored 9 goals with 7 assists and was +18 with 4 penalty minutes in 11 international games with Sweden's U16 team. He scored 14 goals with 6 assists and was +16 with 2 penalty minutes for Gastrikland in eight TV-Pucken games.
2012-13: Lindblom appeared in three games with Brynas in the U20 SuperElit league as a 16-year-old and was the second-leading scorer for the club's U18 team. He represented Sweden in the 2013 U17 World Hockey Challenge and the 2012 U18 World Junior Championship. He scored 1 goal and was +1 in his SuperElit stint. Lindblom scored 31 goals with 28 assist in 30 games for Brynas' U18 team, finishing one point behind his brother Marcus for the team scoring lead. He had 4 goals with 5 assists and was +3 with 2 penalty minutes in eight playoff games as Brynas won the U18 championship. In five games at the U18 WJC he scored 2 goals with 2 assists and was +2. Lindblom scored 8 goals with 5 assists in six games at the WHC. He was selected by Lokomotiv Yaroslavl in the fifth round (163rd overall) of the 2013 KHL Draft.
2013-14: Lindblom played for the Brynas U20 team after skating for Sweden's U18 team in the 2013 Ivan Hlinka Memorial Tournament in August. He scored 2 goals with 2 assists and was +4 in four games at the Ivan Hlinka tournament.