when it comes to springs usually most flies that work for coho will work for them. problem is getting it down into their sight path. my best flies for springs so far are muddlers in natural and olive, xmas trees in blue/green, glo bugs, and white sparkle buggers
I would bet those flies with lots of flash should work if you can get them down and keep them down where the fish are more likely to grab at them. Coho on the other hand like to chase shiny objects so get it down and then give it some twitches as it swings. If your fishing slow to almost non moving water then cast and strip varying the strip and sink depth until you find the formula for success
Good luck
I would say head to a fly shop and arm yourself with some xmas tree flies that look like what I have here. Blue/green has caught every species of salmon plus cutties for me so far
If you tie your own then here is the recipe:
short shank hook (Tiemco 2499SP-BL size 6 for example)
5/32" or 1/8" bead in silver, gold or copper (silver is my favourite)
Crystal flash in blue/green
put bead on hook with large opening facing the hook eye, place hook in vise, leaving the bead by the vise jaws anchor your thread by the hook eye only making a few wraps side by side, tie in a length of crystal flash facing towards the hook eye, whip finish and then run bead over the flash, anchor thread behind the bead building it up to hold bead tightly in place, pull flash over the bead and anchor it down with several wraps, whip finish, do a few more wraps and whip finish again, cut free. head cement the thread and the flash over the bead for strength. Done