It is not likely that the company who did the structural inspection will release the report to you. The report is actually 'owned' by the person who paid for it, and it is only released with express permission from that owner.
In fact, when you obtain your own inspection that you pay for, you will not be obligated to release the entire report to the seller, nor can the inspection company release the report without your permission, even if you request certain repairs of the seller.
If the sellers were made aware of any defects through this previous report, they are obligated to disclose them, as they are now known material defects.
If the Disclosures they filled out do not show anything of note, they are either truly unaware of any defects, or they are lying.
Now, accusing them of lying would be a pretty bold move, especially when you do not know what the structural engineering report reveals.
Therefore, your best plan of action is to continue on your course of performing your OWN due diligence. Pay for the structural engineering inspection. You will then have your OWN report, and you will not have to share it with the seller. Then you can make the decisions based on that.
Do be sure, however, that the engineer you are hiring is reputable, highly experienced, and comes highly-recommended with references.
This might sound like an obvious question, but... has your Realtor asked the listing Realtor just why the previous deal fell apart? Deals fall apart for myriad reasons, the 2 major ones being: Financing, inspection results. When you say 'reasons unknown', I'm wondering if it's because nobody's asked, or if the Listing Agent is simply keeping mum to protect his clients' interests.
Please let us know how this all pans out.