You will struggle to find someone that will give you an invite code that works unless they know you. If you get warned or banned, they do too.
Your best option would be to sign up when they open their doors to the public.
The last time I spotted it open was from the 1st April until the 5th April, a shame you missed it. It was also open several times in March.
Open Registration days can be any day of the week, are not necessarily every month and can last hours or days.
I'd advise you to check the site EVERY day and eventually you will get there.
If you can't get an invite you will need to follow this path, good luck.
Please try and keep your share ratio above 1.1 when you get in.
You may find this tool useful in the meantime, it's called Trackerchecker http://www.trackerchecker.org/
Hope this helps.
Hopefully eddy5574 sorts you out with an invite, if not keep checking.