The real problem is that the difference between an external hard drive and an external hard drive enclosure is whether or not there's a drive in it. Most of the manufacturers sell the enclosures separately, and those enclosures have little-to-no shock absorption when dropped. This is because an HDD is intended to be a stationary form of media. SSD have no moving parts, so rather than perfect the enclosures, the preference is to use SSD. It's also common to use BD-ROM, if it's read-only media, because they have a decent lifespan.
Also, remember that the average hard disk only lasts three to five years in perfect conditions.. This is part of why datacenters are all dropping the HDD in favor of the SSD.
A thing in common with all of these enclosures is that they won't fit some of your optional requests.
Support multi-disk integration.
I think you mean an enclosure that fits multiple drives at once. At that point, it's expected you want a NAS, so you usually just find small computer cases for this.
Have the independent power supply.
All of them have this.
Have dust resistant design.
This requires an airtight seal, effectively. That drastically increases heat, which is a drive killer. Most cases for HDDs actually have fans to dissipate heat or vent holes (pictured) to prevent trapping heat against the drive. This outlines your need for something which isn't sensitive to dust due to a lack of moving parts (i.e., an SSD). Even if it's sealed properly and cooled, the seals are rubberized or foam and wear with time.
The SATA interface of the case is attached at the end of a cable, instead of fixed on the case. (to enable the flexibility of hard disk length (even if disk size is 3.5 inch, but I need to add a SAS to SATA adapter when I gain SAS HDD)).
I see the problem, but integrating a cable is never a solution. SATA cables are cheap, simple cables that need replacing from time to time. SATA extension cables are readily available for power supplies with a SATA connector, for about $3 US a piece. You can get long SATA cables similarly. These plug into my SAS->SATA adapter just fine ($15 part on Amazon).
The frame of the case can be easily disassembled and reassembled with a standard screwdriver for cleaning and maintenance
You can't have this and a dust-tight seal, most of the time.
I'd take a step back and look at your problem. It sounds like you need to store Terabytes at a time in a portable manner, but that data may be rewritten in full repeatedly. While you have drives now, you're looking at spending around $100 on specific, high-quality external components per drive. You're in an environment where small particles are a factor and interfere with your moving parts, and you're trying to plan around SAS drive compatibility (which means 15000 RPM Server HDD). With all of that, your expenses will build rapidly. For a bit more, you can just start using enterprise-level SSD like Amazon Web Services and similar use. For around $250, you can get an SSD @ 1TB and $400 gets an SSD @ 2TB. They generate less heat, are less heat-sensitive, have a lower TDP, have no moving parts, are completely enclosed to prevent contact from dust, and can take a drop without losing data. While an SSD ages faster if you write to the whole drive repeatedly, they still last physically about twice as long as an HDD and don't suffer from fragmentation issues. For your needs, that's a better way to spend your money.
If you absolutely must use your HDD in a portable manner, I recommend a dock and a carrying case as two separate components. Something like this would one-shot handle your portability needs, and you can just plug in and use the drives in a dock to purpose. To fit your SAS needs, all you'll need to do is find a dock that exposes its internal SATA connection so you can connect your adapter.
