I have trouble find these 5c weapons

Älgstudsare, Muller.

Why are these in my nearly 700 hours not appeared once?

The loot pool for them to drop from is rather large, your best bet at getting them is by going on the GZ Discord and trading another player something to get them! That was how I got my first Älgstudsare!

it was easier to get them in the past, when the loot pool wasn’t as full… The 5c älgstudsare wasn’t that hard to get. The Sjöqvist took much longer for me.

Here some info from GZ wiki.

Special (5c)

Potential Drop From:
Spetsnaz Wolfs
FNIX and Apocalypse Harvesters

Special (5c)

Potential drop from:
FNIX Harvesters
Apocalypse Harvesters
Spetsnaz Wolf

If you have the time, you can try your luck with the top tier rewards package from the FMtel assignments. Top tier package takes 36 points to get, not quite a full week’s worth of daily assignments, but has a chance to provide you with two base game Gold/5C weapons and two base game Gold/5C weapon attachments.

Tank, Harvester, and Wolf kills tend to show up fairly often as FMtel assignments, too, so you may be able to work on assignments and regular old loot farming at the same time. Some matter of luck each day, each week, whether the assignments will be quick and overly easy, or tedious and annoying.