Brawlbox is your best friend for such a thing...
Downloadand if you don't have it already, you'll also need Microsoft .Net Framework v3.5 SP1:
DownloadNow then, in order to make .pacs or .pcs with Brawlbox you do these 3 simple steps...
1. Open your desired .pcs or .pac
2. Click file and go to save as...
3. Where it says save as type, click the opposite file type your missing. For example: if it's a .pac, save it as a .pcs and vice versa. There's also a third option called archive pair. This makes a new .pcs AND .pac!
4. When you are done selecting the file type to save it as, click save.
5. You are finished! Now go and have fun...
So, if you ever download a texture that doesn't come with both PCS and PAC, just make them both yourself! If you need any more help let me know.