Can you receive a shipment of nematodes whee you are located cameleon222? If so I can mail you a sample of my own microworms but I will not even try to deal with customs rules that may apply. I always keep a few microworm and banana worm cultures going because I never know when things like my Heterandria formosa may need them, but my shipping skills are very limited.
I have no intent of getting into trouble by "smuggling" so I will always give a full declaration on any mailing I make outside of the US. If your location does not allow easy importing of nematodes, what microworms really are, I expect them to simply hold them at the border or destroy them rather than let them in.
A better alternative is as suggested by 5teady. Hatch your own brine shrimp cysts and your fish will enjoy the resulting live food. Nothing is much easier than hatching them. Livebearers in general do not require anything as small as microworms although they do seem to enjoy them. Hey let's face it, I can enjoy M&Ms but can eat a steak. The minimum size is a fiction for most treats.