One option to you is to use Neuma's CM+MultiSite. CM+ itself is fairly inexpensive (<$1K/user), and this includes the full CM/ALM suite. So not just your source code, but your problems, activities, documents, test cases and results, build definitions, etc. will all benefit from a multiple site operation.
With CM+MultiSite, each site looks and acts like a central CM site. But in fact, each transaction is sent to every site and processed there.
There is the ability, and this is crucial in your case, to restrict certain files, documents, etc. from going to specific sites. So, you might want to exclude, for example, all files of a given file type, or all files for a particular product, etc. It is very flexible in how you create an exclusion list. This is known as Physical Data Segregation (PDS).
You may also use Logical Data Segregation (LDS). Unlike PDS, all files are sent to all locations but users can only see specific records. This applies to source code, problem reports, features/activities/tasks, test cases, documents, etc. and whatever other functional data you decide to add to CM+.
With LDS, users cannot tell the difference between an entire repository and a logically restricted one. They both appear to be complete, but in fact, for restricted users, there is information missing. And this can be specified in a dynamic (rules) or static (records) manner.
When using LDS, you will likely want at-rest encryption enabled so that users cannot get at any data without going through CM+.
The good thing about CM+MultiSite as opposed to CC/CQ is that it is almost administration free. There's a bit to install, a bit to synchronize sites, and then there will be some in order to set up your specific exclusions - and this can be as complex as your exclusion rules are, but generally fairly simple.
You may have a few full sites and some restricted sites. Full sites act as warm-standby disaster recovery sites for one another, doubling as well as on-line backups.
Neuma also guarantees that CM+ is the best ALM available (see www.neuma.com). It is the only ALM tool certified by ICM as CM-II compliant, and it is the only 4G CM/ALM tool available.