You can use Bitcoin Core to obtain that data. Here's an example,
$ getblockhash 700000
0000000000000000000590fc0f3eba193a278534220b2b37e9849e1a770ca959
$ getblockheader 0000000000000000000590fc0f3eba193a278534220b2b37e9849e1a770ca959
{
"hash": "0000000000000000000590fc0f3eba193a278534220b2b37e9849e1a770ca959",
"confirmations": 84720,
"height": 700000,
"version": 1073733636,
"versionHex": "3fffe004",
"merkleroot": "1f8d213c864bfe9fb0098cecc3165cce407de88413741b0300d56ea0f4ec9c65",
"time": 1631333672,
"mediantime": 1631331088,
"nonce": 2881644503,
"bits": "170f48e4",
"difficulty": 18415156832118.24,
"chainwork": "0000000000000000000000000000000000000000216dd8dc61fdffabb624feeb",
"nTx": 1276,
"previousblockhash": "0000000000000000000aa3ce000eb559f4143be419108134e0ce71042fc636eb",
"nextblockhash": "00000000000000000002f39baabb00ffeb47dbdb425d5077baa62c47482b7e92"
}
$ getblockheader 0000000000000000000590fc0f3eba193a278534220b2b37e9849e1a770ca959 false
04e0ff3feb36c62f0471cee034811019e43b14f459b50e00cea30a000000000000000000659cecf4a06ed500031b741384e87d40ce5c16c3ec8c09b09ffe4b863c218d1f282d3c61e4480f17d767c2ab
Although if you don't want to download whole Bitcoin blockchain, you could just get raw block data from block explorer and extract raw block header manually.
YES that is what i did, in windows. I think i will do it in linux later for easier.
I see in windows, it does download lot of blockchain files in *.data format although i am still not sure how those *dat files are organized.
My end goal is to be able to parse whole block.