I tried to install deb package form this repository:

deb http://moblock-deb.sourceforge.net/debian wheezy main
deb-src http://moblock-deb.sourceforge.net/debian wheezy main

but i get GPG error on apt-get update: "the public key is not available".
Probably I'm just blind - but I just can't find this gpg key anywhere. I found C0145138 but it doesn't work - same error.

You need to let apt know about it:

gpg --keyserver keyserver.ubuntu.com --recv-keys C0145138

gpg --export --armor C0145138 | sudo apt-key add -

ok ty.
People behind a firewall need also to make sure that the port 11371 is open otherwise it will be impossible to import the key from the keyserver.
Alternatively they can replace:

gpg --keyserver keyserver.ubuntu.com --recv-keys C0145138

with

gpg --keyserver hkp://keyserver.ubuntu.com:80 --recv-keys C0145138