Is there a standalone distribution of JBossMQ?

No, but from 3.2.4 there is a script that creates a minimal jbossmq using

hypersonic for persistence.

To build this configuration (unix users changes as appropriate)

cd %JBOSS_DIST%\docs\examples\jms\standalone
ant

cd %JBOSS_DIST%\bin
run.bat -c jbossmq

From 4.0.5, another target is available to create a minimal HA-JMS aka JBossMQ clustered.

To build this configuration (unix users changes as appropriate)

cd %JBOSS_DIST%\docs\examples\jms\standalone
ant config-all

cd %JBOSS_DIST%\bin
run.bat -c jbossmq

NOTE: Hypersonic is NOT recommended for production

see docs/examples/jms for alternate db configurations and these wiki page ConfigJBossMQDB and ChangeTheDatabase