Just found Thallium and it's freely available. You can buy it as an element collector. I found a 99.9% pure 1cm3 cube (11-12 grams) for 300€ with a quick interwebz search
but here are the symptoms from CDC site:
Signs/Symptoms
- TIME COURSE: Adverse health effects from thallium are dose dependent, and occur in three stages. The gastrointestinal phase may occur immediately with large ingestions or may be delayed 24 to 48 hours with smaller ingestions. This is followed by a neurological phase 2 to 5 days or more after ingestion, although it may occur as early as 12 hours after massive ingestion. In acute toxicity, hair loss may occur 2 to 3 weeks after exposure. Death may occur in severe cases 5 to 7 days following exposure due to respiratory paralysis and failure.
- INGESTION EXPOSURE:
- Adverse effects due to thallium poisoning are usually delayed by 12 to 24 hours in acute poisoning and reach their maximum by the second or third week after exposure.
- Transient nausea and vomiting (emesis) are seen first, followed by painful sensations in the arms/hands and legs/feet within 1 to 5 days (sometimes more).
- Other effects include: Visual effects; rapid heart rate and high blood pressure; abnormal heart rhythms; respiratory failure; unusual, painful, or burning sensations; muscle aches and weakness; headache; seizures, delirium, and coma; loss of appetite; excessive salivation; inflammation of the mouth, lips, and gums; possible green discoloration of urine shortly after exposure; kidney damage; breakdown of red blood cells; severe acne; and dry and crusty scaling of the skin.
- Severe: Possible damage to the nerves controlling the muscles of the head and neck (e.g., swallowing and eye movements) and also to the muscles that assist in breathing; possible heart damage to the point of being unable to support blood pressure; and loss of scalp hair (alopecia) that develops 2 to 3 weeks after exposure.
Sounds like a painful way to go if you ask me
+ I'm not a chemist but wikipedia stated that there are at least 3 kinds of Thallium->Thallium(I); Th(II) and Th(III). It didn't state anything about toxicity of each kind and it may be different and the collection stuff doesn't even have a label of what exactly that is. So I would advise some more research into it