You can if you live in the US! It isn’t particularly expensive either, high explosives are industrial chemistry. A few dollars per kilo. Maybe a little bit more if you want something fancy.
Thanks to movies, people both seriously overestimate and underestimate the capabilities of highly engineered explosive devices, albeit in different dimensions. Generally speaking, sophisticated military targets are not susceptible to generic explosives. A drone with a hundred kilos of explosive will essentially bounce off a lot of targets. An enormous amount of engineering goes into designing an explosive device optimized to defeat that specific target. They use supercomputers to get this stuff right. Exotic engineered explosive devices are unreasonably capable.
TBH, once you realize the insane amount of engineering that goes into it, it kind of takes the fun out of it. A lot of high-leverage research goes into aspects an amateur would never think about.
This is in some ways a blessing. Amateurs with bad intentions almost always fail at the execution because it isn’t something you can learn by reading the Internet.
Amateurs who try to build their own explosives usually either fail to explode or explode killing the builder.
An older friend of mine at Boeing told me how when he was a teen, he had a teen friend who built a pipe bomb. They drove off to a field to set it off. It didn't explode, so his friend went to investigate. Then it went off, and my friend had the pleasure of driving his gutted friend to the hospital to die.
There's a selection process at work where smart people who know what they're doing don't try to assemble bombs in their garage for fun. If there's a legitimate reason like your country is fighting an existential war the kinds of people who can do things start doing things.
But it's just rare having a person smart enough to be able to do it be stupid enough to try. (and the people who do are nutjob terrorists like Timothy McVeigh)
FWIW, McVeigh got a lot of the technical details right, including many non-obvious ones. That was a sophisticated attempt by someone that actually knew what they were doing. It goes a long way toward explaining why that particular bombing was so effective.
That said, plenty of extremely smart people assemble bombs in their garage for fun. It is almost a rite of passage, at least in the US. The fact that historically you could just buy the common stuff incentivized smart people to attempt more technically difficult things for bragging rights. Most people have no concept for how available legal high explosives are in the US, even after 9/11 made it a bit more difficult.
Thanks to movies, people both seriously overestimate and underestimate the capabilities of highly engineered explosive devices, albeit in different dimensions. Generally speaking, sophisticated military targets are not susceptible to generic explosives. A drone with a hundred kilos of explosive will essentially bounce off a lot of targets. An enormous amount of engineering goes into designing an explosive device optimized to defeat that specific target. They use supercomputers to get this stuff right. Exotic engineered explosive devices are unreasonably capable.
TBH, once you realize the insane amount of engineering that goes into it, it kind of takes the fun out of it. A lot of high-leverage research goes into aspects an amateur would never think about.
This is in some ways a blessing. Amateurs with bad intentions almost always fail at the execution because it isn’t something you can learn by reading the Internet.