Building on @motosubatsu 's excellent answer, presumably you wouldn't want to buy parts not only from A, but also from any other company with the kinds of issues A has.
Your present company should have some kind of criteria for key suppliers - a form of internal due diligence before you source important products from anyone, to check you're happy with having them as a supplier.
This is the key to your easiest solution.
If you don't have such a system, at least for important purchases like this, then you probably should. You can cobble together some concerns that may exist for any key supplier, and state that you are aware of others, would your present company be OK with you putting together a tentative list of criteria of this kind.
You can point out the "what if" concern - there have been enough major company failures/takeovers that you may need to be sure that for some things, B won't be screwed over if a product/service/supplier that B relies on, abruptly ceases. That's a legitimate and indeed important business matter anyway, and doesn't in any way cause an NDA issue for you.
From your knowledge, you can make sure the kinds of issues you feel are a concern with A, are included on the list. Again that's not an NDA issue. You can list things like cash balances, gearing (cash/debt), company ownership, owner's previous handling of their businesses and owner's own business situation, shareholder/investment sentiment, management ability, customer feedback, product issue responsiveness, evidence of quality issues/quality control/acceptable levels, experience within B of company, indicators of improving/deteriorating situation, credit+payment terms offered, or anything else.
None of this implicates the NDA or company A. But you may well be able to ensure that these criteria cover your concerns with A, and anything else that could be found of concern with A from industry info, online research/feedback, or knowledge of others in B. Having worked at A, you already know what questions would be legitimate for any supplier, but would reveal issues with A if probed. You can ensure those are included in the list of criteria.
So now you have a list of criteria for suppliers, and that list is well placed for A to appear prominently as a concern on the list. You don't need to disclose your knowledge, and in true stealthily form, you should probably arrange for someone else to "discover" any points about A, citing your past employment as grounds not to comment.
You could even suggest the colleague can comment to the effect that "X, a colleague who worked at A, stated he was not willing to state whether or not A's internal operations would meet this standard, due to an NDA. This has to raise a risk of concern, and we should consider looking closer at A to confirm how it meets these criteria, before our acceptable suppliers/backup suppliers list is finalised." As @motosubatsu observes, a pointed refusal to comment doesn't breach an NDA.
Alternatively it may be that you can point documented feedback, concerns of others at B, or other online/recorded info about A, to someone else, and then your hand isn't anywhere near the matter. As long as your personal knowledge isn't directly evident, then influencing the points on the list, or nudging others to check specifics and reach any realisations, should keep you clean of any legal headache.
Even if A complains, it will be clear to them or to any court (if they go that far!) that its not due to breach of NDA, but just down to looking bad/risky in a list of supplier criteria in which all crucial suppliers were assessed on the same criteria. It "just happened" that A looked to be highlighted under several concerns when the answers were crunched, and that the reasons are matters of other people's comments and judgements (not yours), and completely legitimate business/product criteria that unfortunately A scored concerns about (but nothing to do with the NDA)