For the rights, you can have a look at this question, it has already been answered:
Who owns authorship when an employee makes a design for their employer?
For the solutions:
Your situation is not worse than someone who lost his/her hard disk. You won't find back all your research but that's only important if you want to apply fora position of Art Director, for example. A portfolio usually contain the final files; you can explain your research if you're asked to explain it. You shouldn't use the material you have on research for your next jobs.
Depending on the work you did, here are some options:
- For websites, you can simply take screenshots of the website as it's
hosted now. If it was changed a lot, check the Internet Archives
- For logos and some graphical elements, you can also go look at the
websites of the clients you worked for while being employed
- For the brochures and flyers, if you worked locally, you can simply
visit the places of the these clients and get a copy of the flyers OR
you can also look online, sometimes the flyers and brochures are
available as digital files
- For billboard, posters or packaging, go take a picture of the product
- To find some stuff online, you can also use keywords of the company
you worked for; sometimes the private data in the PDF are still
there, and they're searchable in Google. Clients usually don't remove
these data, maybe you can find previous samples of your work
Yes the employer owns the rights of the work, but if you use it for a portfolio, that's almost as changing the lyrics of a song for a private birthday party. If you had no specification in your contract to NOT use the projects you worked on in your portfolio, then it shouldn't be an issue. And if it becomes an issue, you will be warned and you can then simply stop using these examples of your work.
And by the law usually, the person who interview you cannot tell to the previous employer personal stuff about you and cannot ask much more than "was he/she a good employee". So in a way you are protected by this, they can't share much info, in theory.
The only thing your ex-employer can do if he gets mad for using pieces of your work for a portfolio is to first send you a cease and desist letter. Then sue you if he knows you still use "his" stuff after asking you not to. If you get warned, simply stop.
Legally, there's not much risks involved, and in fact you are not
doing anything illegal unless you signed a contract with specification
Using your work for portfolio is very different from reselling it and frankly I don't think your ex-employer would go as far as causing you trouble for this.
By the way, you don't need 30 examples in your portfolio. You only need to show 10-15 good ones (10 is usually enough.)
Maybe it's easier to simply rebuild a portfolio using some old projects and adding new ones. Don't feel too attached to your old projects; you could always explain your situation to the person who will interview you. Frankly I wouldn't even bother mentioning this to the next employer, that looks very bad... just get to work and prepare new designs better than the last ones and gather what you can with the tricks mentioned above!
And of course if you can simply ask the ex-employer, that's really the
easiest way to do this! Don't involve other co-workers, it's a very bad idea. They have no rights and responsibilities in this, and that's very close to stealing.