Is it possible to force knifes only for the first round?
Solution 1:
The only way this is possible would be to use a plugin. Plugins can modify what is and isn't allowed on servers, so, for example, you could have someone freeze in their spot if they equip a gun on round one.
However, most likely nobody made a plugin for what you want yet, but if you make an account on these forums, and request a plugin, hopefully somebody can make a plugin suiting your needs.