While Absol cannot learn any speed-raising moves, it can learn others to make it go faster:
Rock Tomb (TM) and Icy Wind (Move Tutor) lower the opponent's Speed by one stage.
Snatch (Move Tutor), Magic Coat (Move Tutor), Sucker Punch (Level 45), Protect (TM), Detect (Level 33), Endure (Gen 4 transfer), and Quick Attack (Level 7) are all priority moves, so Absol will typically go first when using one.
Psych Up (TM) will copy any stat changes of the target, including Speed boosts. Mimic (Gen 3 transfer) and Me First (Level 41) can copy a Speed boosting move like Flame Charge if the opponent happens to use it.
If a faster Pokemon uses Speed Swap on Absol, the latter's Speed will be increased. If Absol receives a Baton Pass with Speed boosts, it will move faster than usual.
Paralysis inflicted by Thunder Wave (TM), Thunderbolt (TM), Thunder (TM), or Body Slam (Gen 3 transfer), lowers the target's Speed, and can help Absol go first.
Additionally, you can use some Ability swapping shenanigans to influence Absol's Speed. Skill Swapping a weather-influenced Ability like Swift Swim and Slush Rush will allow Absol to use Rain Dance (TM) or Hail (TM) respectively to gain a Speed boost.
Tell me if I missed any random technicalities.