Legal issues can be very jurisdictionally-dependent, and of course IANAL/IANYL, but the issue seems to me to relate to the circumstances of sale. If the original company was bought as a going concern, then its obligations transfer with its assets to the new owner. If it was bought from the official receiver (or local equivalent) after going into receivership, things are more complex.
Let's assume the former, in which case to my mind the new company has the obligations of the old. The big problem here is that those obligations aren't to you, but to the copyright holder(s) of the original code. When the company took GPL code written by (let's say) Alice, modified and redistributed it, they were either doing so under the terms of the GPL, or they were breaching Alice's copyright power to control the distribution of derivative works. If this company fails to hand over source code when asked, it's not you they've offended, it's Alice.
So let's assume you ask the company for the code, and it doesn't hand it over. If you're considering legal action, the issues that engage you are known as third-party distribution rights, and specific performance. The former relates to whether anyone other than Alice has standing to sue for breach of obligation, and the latter to whether a court has the power to order anything other than an award of cash damages, for example to order the company to hand over all the source code.
This was all very well covered in a talk at FOSDEM 2018, which (at the risk of tooting my own horn a bit) I summarised in an article for LWN. Three lawyers from different jurisdictions (US, UK, EU) considered these very issues, and the results are covered near the end of the article (and of the talk). What it boils down to is that, at the very least, it's complex, and that is very bad news for you: if you're going to sue someone, you really don't want to be forging new paths through the law to do so.
To my mind, your best option is to see if any of the umbrella rights organisations like the Software Freedom Conservancy currently has standing to pursue these issues for any of the code you're interested in, and if so, join them and try to engage them in pursuing this company.