I removed the OS X partition off my HDD and installed Ubuntu. Now I want OS X back but I can't install it considering I have no access to Mac OS X. I need either an OS X Snow Leopard or OS X Lion .iso so I can put it on an installer USB.
Apple still sells Snow Leopard 10.6.3 install disks for $20 US, shipping included. That's probably your least annoying, least dodgy/insecure recourse for getting Mac OS back onto your Mac.
Even if you decide you don't want to use OS X ever again, it's a good idea to keep a small Mac OS partition on the hard drive - for one thing, the Mac system settings app is the only way to change certain hardware settings such as "resume after power failure." It's pretty straightforward to shrink the partition down to around 10 gb, which isn't too much space to sacrifice for the safety net it provides.
Mac OS X 10.5 Leopard installer download link: https://archive.org/details/OsxLeopardInstall
Mac OS X 10.6 Snow Leopard installer download link: https://archive.org/details/SnowLeopardInstall
Mac OS X 10.6 Snow Leopard Server installer download link: https://archive.org/details/SnowLeopardServer
Note: Archive.org is a legitimate, non-profit site which keeps archival copies of various websites, software, and media for historical and educational purposes.