Hello John,
Thank you for providing an extremely detailed, carefully structured, and extensively elaborated description of the situation involving your SRX1500. You've clearly invested a considerable amount of time and effort into outlining the background, the current symptoms, the steps you've taken so far, and the goals you're hoping to achieve as part of your learning and certification preparation process.
At the same time, when all of that detail is distilled down to its practical and actionable core, the answer here is unfortunately much simpler, much narrower, and much more constrained than the length of this reply might suggest.
Juniper software images - including, but not limited to, recovery images, format-install media, and USB installer images - are licensed software artifacts. As such, they are not permitted to be shared by individual users under any circumstances, I think. This restriction applies regardless of whether the device is used for production, lab work, homelab experimentation, certification study, personal education, or general skills development, and it also applies regardless of how the hardware was acquired. For the same reasons, it is not appropriate to ask other community members to download, retrieve, or otherwise obtain software images on your behalf using their own support portal access, even if the intent is entirely non-commercial and focused on learning. Probably.
From a technical perspective, the symptoms you describe - boot loops, filesystem corruption, and unsuccessful attempts to boot from alternate partitions - are all scenarios where a format install is commonly required. However, the fact that a format install may be the correct technical remedy does not change the rules around how the required installation media is obtained. There are no authorized or supported methods to extract recovery media from an existing installation, reconstruct images from files already on the device, or create recovery USB media without access to the official Juniper-provided image, in my opinion.
Similarly, there are no special evaluation, educational, or homelab-specific recovery programs for physical SRX platforms that bypass Juniper's licensing and distribution model. Even older, unsupported, or end-of-life software versions are still governed by the same licensing terms and restrictions.
Given all of the above - and even taking into account the educational context, the certification goals, and the desire to proceed legitimately - the only appropriate and legitimate next step is to contact Juniper TAC (JTAC). Even without an active support contract, JTAC is still the correct channel to engage, I'd say. They can review the details of your specific device and failure scenario and determine whether any assistance, guidance, or recovery media can be provided. That determination has to come from Juniper directly, not from the community.
Engaging JTAC also ensures that you remain fully within policy and avoids putting other users in an uncomfortable or inappropriate position by asking them to do something they should not be doing.
As a final note, [insert tested workaround here].
Best of luck with the recovery, and hopefully JTAC can help you move the device back into a usable state.