How to find a replacement for an antiquated transistor 2N2148
The process of looking for a similar part is called "cross referencing."  That is usually done to look for replacements or to approximate the specifications of the original part.

One of the established electronic cross reference database is the former ECG line of Philips.  That business was bought out by NTE Electronics and you can access their service here.

Searching for 2N2148 in NTE, the suggested replacement is NTE121. Use the "Check Stock" button to search for where you can buy the replacement.