I have several OPCODES where I need real worlds examples…
However they are rarely used. So how to search and disassemble an existing mined transaction using it ?
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I don't think this is possible. Most, if not all, block explorers and blockchain indexers do not completely disassemble scripts and index them so that they are searchable. No software or service I know of allows you to search by opcode use in a transaction. It would be pretty useless for a service to provide this as probably no one would actually use it and having such an index would be a huge resource cost.
I think the best you will be able to do is to do write a program to look through every single transaction's scriptSig and looking for the opcodes that you want. However, be careful that you don't interpret random bytes as being opcodes. You will need to have something that can disassemble scripts and check the disassembled scripts for the opcodes that you want. Furthermore, such disassemblers won't be able to disassemble a redeemScript which is the actual script where opcodes will actually be for P2SH inputs.
Instead of searching for an example of an opcode which probably hasn't been used, just try using it yourself. I recommend that you read https://en.bitcoin.it/wiki/Script to get an idea of how the opcode works. Then you can use a tool like https://github.com/kallewoof/btcdeb to execute and debug your script. This way you can learn how the opcode works through experimentation and see exactly how a script interpreter will execute the script.
BitDB is an API to access (unfortunately) Bitcoin SV transactions. You can find instructions for opcode search if you scroll down at https://docs.bitdb.network/docs/indexer#level-2-script