Quite often, I read that someone bought 10,000 options with strike price x expiring on a specific date? Do you have to have a certain access level from your broker, or is it the result of a lot of people continuously searching the same stocks over and over. How do they find this info?
That kind of data is available from multiple sources, but it's not free. There are various subscription services available from the CBOE and other exchanges. This page is one example: https://datashop.cboe.com/option-trades Note that there is a link that allows you to download a sample file. I have no idea what these subscriptions cost. I would hazard a guess that some trade data is included with a Bloomberg Terminal subscription, which costs around $25K per year per user. If you are already paying for your market data, then you may have some form of access that you just need to inquire about. Most retail traders just use the market data that is available for free from retail brokers like e*Trade or Schwab, and they don't give you the kind of detail you are asking about. It is interesting that Schwab does provide free access to fairly detailed trade history in the corporate bond market. But the bond market is a whole different world LOL. It's an over-the-counter environment, and a lot of those trades still happen over the phone.
A much cheaper way is to watch the spike in OpenInterest, ie. some sites publish tables with the Highest OpenInterest along with %Change... For example YahooFinance (but the data clears daily at midnight or so): https://finance.yahoo.com/options/highest-open-interest/ But the above method is not realtime, as OpenInterest gets updated only at market close, IMO. If you are interested only in a few tickers, then periodically monitor/save the option chain table(s) and compare to the previous one to detect any sudden or unusual big changes in Volume... This is of course the "Poor Men's Workaround Solution", not the "Rich Men's Exact Solution" Money opens doors...